Yes, it is. The 3800 X2 is 2.0GHz compared to the 3800+'s 2.4GHz. However, the dual core should outperform it in multi-threaded games and when doing multiple intensive applications at once. If you're just gaming without much of anything going on in the background, the single core will outperform in this case.
It's cheap because it's dual core and I believe the Venice is a lower end core. If I remember right the San Diego is the higher end one. Still an great proc for the money, can't go wrong with that one if you're not multitasking or encoding video all the time.
Games don't take advantage of dual core yet, but hopefully soon. So if you want the best bang for your buck gaming processor I'd look at the 3700+ and OC it slightly to 3800+ speeds, that way you get doubled the L2 cache of the 3800+. Also, look at Socket AM2, not Socket 939, infact AM2 is future proofing your system and remarkabley cheaper than some of it's Socket 939 counterparts.