Um, its nowhere close to being done, though.
The 993 started in 1993 and lasted til' 1998. The 993 GT2 was built from '93 until '98 where it got one last upgrade to 450Bhp from 430.
The 996 was 1998 to 2004. The 996 was nearly the same. It wasn't until around 2004 that it went from 462 to 483Bhp for 1 final year.
Thus, following the last 2 GT2s, I would assume the GT2 of the current era will be the same. It won't receive any upgrades until the 997's final year of production, which probably won't be until 2010 or 2011 since it just got a facelift last year (and also because the 996's small "re-design" last 2 years).
BTW, your theory on the 997's production ending due to the years is a tad off. The 993 last 5 years, the 996 lasting 6 (7 since the GT2 was around as an '05 model), & the 997 has been around for 5 years.