Of course they make it up, I saw the same when I had a Toyota Starlet SR in the past. Admittedly not the sort of car that alot on here would choose, but book was quoting prices around £2500 when I came to sell because of the standard models. However when I checked prices they were going for (and also taking into account mine was relatively low milage) I realised that was a load of rubbish. I ended up selling the Starlet for £3300, I even had a couple of Toyota Engineers interested (one from down south, and one local who came and test drove).
However it also has to be said the prices of Mini's is fairly over the top at the minute, considering comparable cars. Understandably they are a Premium brand but it would very unusual if their prices didn't come down at some point, what I'm sure most people would agree is they'd be happier if Book prices were reduced gradually, and with checks done on real world prices, rather than just either changing it one month by say a £1K, or deciding they'll PUSH prices down to something THEY reckon there worth but that nobody else agrees with.