Floyd's aero bars were tilted just a fraction too high... they have lowered them just millimetres to be at the max height within the regs.

There are many regs around competition events as Veronica said...
weight of bike
crank length
seat height
how far/back seat is allowed to be
distance between seat and bars
the size of the triangle

... and on it goes...

If you turn up to an event and the commissairs (sp?) measure your bike and it doesn't meet the specs, you will not be allowed to race.