But you're missing the point...even though, hardware-wise, it's made of PC parts, it's NOT
a PC, so don't compare them directly. BTW, many of you said than in days of Naomi things were different...well, not really. Naomi hardware was exotic, but not that powerfull - Kyro/Kyro2 cards used in PC (of the same heritage as Dreamcast/Naomi) were faster than its GFX part.
The thing is...arcades/consoles can:
1) Have overall hardware design/architecture geared towards processing games (obviously not the case here, but when one looks at PS2...)
2) Run o lightweight operating system
3) Have games optimised the **** outta them - you must develop only for ONE, SPECIFIC hardware type - you don't have to care about how the games scales, so you might do things that, yeah, are possible on comparable PC, but nobody does them because the game won't run acceptably on slower machines. Oh, and you can play with hardware a bit more directly when you're sure what it is...
Just look at PS2. Its hardware specs aren't very impressive...but it beats the hell out of one of my PCs which is theoretically around two times faster.
And one important point - it's safer for them to go with hardware that is for sometime on the market...reliable and so on. Might be important, especially given very "unfriendly" enviroment in which many of the arcades must work
And, more seriously - no surprises. Going with cutting edge stuff migh be one of the things that caused for Sega finacial troubles.