The ten speaker set up was standard on 05 plates but penny pinching VW cut this down to 8 speakers from around 2006 onwards.
My 2007 model year still has 10 speakers. Wasn't the three door GTIs which only had 8 speakers?
The midrange speakers were only discontinued from MY06 for RCD300 / 500.
Over and above this you might have the optional amp (have a look under the plastic cover under the passenger seat if its there or not), but I don't think this was that well reveived by those who paid for it.
That was only with the optional factory fitted 'Volkswagen Soundpack' - and yes, it was utter shyte.
I found that the speaker set up is pretty good, but the HU makes a huge difference. When I got my car it had the terrible RCD300 (and the rcd500 is the same except it has the 6 disk changer) and I thought the sound system was rubbish, lots of distortion and vibration if you turn the volume up. I upgraded to the MFD2 sat nav and the improvement in sound quality was like night and day. So speakers are fine unless you are really into your music but HU is the limiting factor.
Humm, even with the factory fit SatNav and 10 speakers, I still find the speakers quite poor. 
Its subjective but I assure you the MFD2 sound quality is a quantum leap over the RCD300 it replaced.
Being an 05 plate it will have certain 'features' that the accountants removed from later models like blue tinted glass (rather than green - looks nicer IMO), the aerial is integrated into the rear screen, 10 speakers as standard, silver ashtray cover, three reading lamps at the front vs 2 in later models etc 
The blue tints didn't look right with certain colours,
hence why they changed to green. 
The radio aerial is still integrated into the rear screen, on all models - but some have an additional one on the roof too.
The silver ashtray cover and surround is quite an easy retro fit - but not cheap though!
The blue tint looks cracking with red.

Again though thats somewhat subjective.
As for the rear aerial, I know that for the MY04 like mine that if you had nav or phone prep from the factory there was an aerial on the roof but otherwise there wasn't. On all the later models (maybe from MY05 onwards

) they all have at least the bee sting so something changed. Seems odd that they would provide the more expensive rear screen version AND the bee sting if there was no need.
This list of MY changes certianly indicates that the rear screen aerial was discontinued, but maybe for factory nav the roof aerial is used only for nav and the radio is still picked up from the rear screen?
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MY05 Changes were :-
• Lockable glove boxes, chrome handbrake button and chrome gear lever collar.
• An external temperature display displayed in the entry level MFA (S & SE) only
• Seat belt audible warning on front seats.
• VW headlight bulb cover and silver rather than dark grey headlight interiors.
• 2005 model 1.9 TDIs also had just TDI on the back rather than the 1.9 TDI of early models.
MY06 Changes were :-
• Radio / Navigation knobs now with chrome plated finish
• Gear Shift Cover with a Chrome plates surround
• Change to door side trim
• Open ended spanner in toolkit discontinued
• "Assistance in Europe" manulas discontinued in Handbooks
• Roof Aerial in conjunction with RCD300/500/Plus replaces aerial in rear windscreen
• Mid range speaker discontinued in RCD300 and RCD300 Plus
• New operating controls on multi-function steering wheel.
GTi specific:
• New Leather steering wheel with tiptronic paddles for DSG models
• Front foglights changed from projection to reflector technology
MY07 Changes were :-
• Automatic employment of warning lights under emergency braking
• Rear headrests reduced in size
• Whiplash optimised front headrests (replaced active headrests)
• Change to front courtesy light – discontinuation of the middle lamp and housing is no longer lacquered
• Radio and navigation systems – Silver Buttons
• Change of icon on the lock/unlock button
• Location of the airbag warning label will be on the B pillar rather than next to the windscreen
• Centre console foot space covering for front passengers in black only (beige and grey discontinued)
• Soft Touch Plastics in doors removed
• Leather armrest replaced with leatherette
MY08 Changes were :-
• Rod aerial replaces ‘shark fin’ aerial when the optional satellite navigation system is ordered.
• Introduction of new generation immobiliser. Generation IV.
• AC button instead of ECON button for climatronic air conditioning
• New feature on climatronic air conditioning unit. Air quality sensor with automatic changeover switch.
• Change to the symbols on the indicator/wiper lever.
• The black centre armrest with fabric covering will be changed from a ’fell’ seam to a 'join’ seam.
• Removal of optional factory fit telephone preparation. Available as aftersales fit only.
MY09 Changes were :-
• Symbol change on interior monitoring button for anti-theft alarm
• Glove compartment handle changes from chrome to trim colour
• Electric sunroof button changed
• Mirror heater dial position changed from 12 o’clock to two o’clock
• RCD 210 with 4 speakers replaced RCD 300 with 4 speakers
• Hill-hold function standard on 6 speed and 7 speed DSG
• Symbol change on headlight switch
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