Man it's like this:
Fighting games are the new "popular hobby", especially given the fact that most of the games released since SF4 (including SF4) are easy accessible games that have been dumbed down for the newer generation of fighters... It's not on the verge of death, but it's more of a spike per sé, where there's a quick boost in sales and hype, but overtime, that spike is gonna drop on the other side, and make way for the "new trendy gaming genre"... It's nowhere near what it was back in the "golden era" where Capcom and SNK and a plethora of other gaming companies spewed out fighters for saturn, ps1, ps2, dc, n64, xbox and even gamecube... Now, only a few games really come out, and those that give much hype (heavy marketing = popularity), money, and has a huge amount of support for the online community get mad play and the others, well it kinda depends on the FG community that supports that particular game... That's why so many people get on the SF4/Tekken train and not the KoF/VF train... There have been people who make excuses saying "I don't play 2d fighters", but still get on SF4, or they say things like "I always loved KoF/VF over SF/Tekken, blah blah blah", but barely get on KoF or VF...