OK.. Finally... Someone actually gets my point.
Sure, SLI takes up more PCB space, but so what? Most gamers don't use many PCI slots anyway. A sound card... May-be a wifi card. Other then that... you're not using PCI 56K modems or PVR's or SCSI / RAID Controller cards... So the space is available...
As far as making better 1 card solutions goes, "They are!" But, they are so freakin' expensive. $750 USD? $800 USD $1000 USD?
Benchmarks show that (2)7800GT's on a good motherboard out perform all of the latest X1800XT's & 7800 GTX's in all benchmarks.
Why spend $800 on a single card when you can buy (2) and SLI them for $200 less and get much better performance... specifically at higher resolutions...
Yes, overall on the grand scale of things... SLI is bogus... But, there are certain niches that it can benefit. And what i've described in several posts in this thread is were you benefit from SLI.
Now, if the X1900XTX or 7900XT's came out and cost $500 USD and out performed the SLI'd 7800GT's by a long shot, then my theory would go to heck... But, I don't see that happening...
The next GEN cards will be over $600 USD... As much as $900 USD. Keeping the 7800GT's a good choice...