not quite, if the texture unit count wasn't soo important then ati wouldn't (or so its rumoured) be doubling the texture unit count for its next high end chip (rv770), going from 16 in the current rv670 with 320 shaders to 32 (tmu's) and 480 shaders in the rv770.
With some quick and rough maths the ratio of texturing units to shaders is 1/3 higher. If implemented in the 3850 & 3870 (and 2900xt and pro too) that would mean something like 21.33 tmu's instead of just 16. Of course you can't have 0.33 tmu's but this is just hypothetical after all. (note ati's texture units are a bit more beefy than nvidias, so less are required for equivalent performance, although nvidia still has a big lead here)
"The 320 "stream processors" on the R600(HD2900)/RV670(HD3800) are actually just 64 processors each capable of 5 operations per clock cycle under ideal conditions."
Thats not quite true. There are 64 more capable shaders, each with their own group of 4 less capable ones. Another unit attempts to feed them with instructions cued in the best possible (most efficient) order looking 'forward' 5 instructions. This is complicated, and was often highlighted as a possible issue when the r600 was released but driver revisions (poor early performance and some plain broken games performance) I would speculate have gone a long way to preventing chronic stalling here.
"The texture unit advantage of the 8 series isn't all that important. It's the ROP count and design that gives 8 series cards the advantage when AA is applied."
The 8 series generally has an advantage when AA (and even AF) is NOT applied. Indicating that either shaders or texture units are lacking. Given r600 and above only have 16 TMUs and an apparent horde of shaders, it would appear that more texture units are lacking. Having the shaders clocked seperatley from the main core shouldn't be an advantage for Nvidia when ati have more but slower clocked shaders. 3Dmark06 feature test results do show some very capable pure shading power from the r600 & rv670 cores. So on that point it's pretty moot.
As far as ROPs go, its not quite true that the 8 series has an advantage in having more of them, rather that they are used to implement AA, whereas for DX10 ati cards they 'just' shuttle pixels out to the monitor. So comparing ROPs here is a bit irrelevant.
However, the poor price/performance of the ati 2900 & 2600 xt & pro, and no competitor to the 8800gtx last year really helped 'the way it's meant to be played' take off. Games are developed with nvidia cards in mind, make of that what you will, but in my opinion that matters more than lacking texturing power.