Using ATI hardware as an example, in 2007 there was decent 2D support for the 3xx/4xx GPUs (ie the 2002-2004 SKUs), experimental 3D for the same parts, plus the initial RE'ed avivo driver for 5xx. The only fully supported parts were r2xx and earlier, which were ~6 years old at the time. This matches what you are saying.
2-1/2 years later, the graphics stack has been rebuilt around a common memory manager, which is a critical pre-requisite for further 3D work, 2D has been largely rewritten to make use of the 3D engine, *and* hardware support has gone from being ~6 years behind to ~6 months behind on average, in the sense that Evergreen has had modesetting support for a while (3 months behind), power management on EG is happening in sync with older parts (6 months behind), but acceleration is just staring to light up now (9 months behind).
Measuring status at the start of a project is fine, and it would be totally fair to say that open source development was 6 years behind in 2007 when the project started, but given the amount of catch-up in the last couple of years it's really hard to argue that your "years behind" statement applies today or will apply in the future.