We tried a letter system where the letters had real meanings in and of themselves, no one liked it 'cause no one knew what they meant. Whether you like the current system or not, everyone pretty much knows what it means by now.
Comparing graphics that way is arbitrary, and quite frankly, stupid. We review games for their target audience. We're not reviewing Wii games for 360 owners or vice-versa. I would no more mark down a great-looking Wii game for not being in HD than I would a great dual-analog first-person shooter for not having mouse/IR aiming. You can't mix your standards like that.
Besides, PC would always win those comparisons. ;)







