It's not really the warranty that should be the issue.
The two year brake fluid change (BFC) was introduced on an industry wide basis on the simple grounds of safety. Cass rightly pointed out that it will cost you though!
Brake fliud is hygroscopic - that is, it actually absorbs water from the atmosphere. This degrades the brake fluid in a number of ways. Firstly, it lowers the boiling boint of the brake fluid. This can lead to vapour lock, where the gas prduced from the boiled brake fluid then becomes compressible (where liquids don't), and therefore does not transmit the hydraulic pressure applied by the pedal at the master cylinder. Another problem is the water content will cause internal corrosion of all brake components, including the master cylinder, ABS/ESP modulators, load sense or pressure limiting valves, wheel cylinder and caliper pistons. The corrosion can damage internal seals in these components, causing leaks, and in some instances, will completely seize pistons etc. In the old days, a rear wheel cylinder could be had for £20, but ABS modulators are £750 upwards, and disc calipers can be £70 upwards!
I personally would strongly recommend not to exceed the 2 year BFC. I actually change mine every year, but then track days, high speed Autobahn blasts, and mountain hairpins certainly test the brakes!
Rgds
