Online multiplayer matters some, but pretty much only for traditional PC genres (FPS, MMORPG and RTS) that are annoying or impossible to play multiplayer without online. Online gaming can be fun with other genres (Sports, fighting) but aren't necessary and may not be worthwhile when considering the issues (lag, annoying online communities, inconsistent matchmaking, etc.) Why not just play with friends live when you can?
And Consoles have tried to incorporate online gaming since at least the Genesis/SNES (remember x-band?) The closest thing to success has been with the x-box and x-box 360 which have made online gaming the cornerstone of their brand. The x-box was so successful it sold 25 million consoles and lost billions of dollars. The 360 is so successful its stalled at 10 million sold and has yet to turn a profit. There's little evidence that online gaming is the future of console gaming. On PCs, online gaming has been HUGE for over a decade (starcraft, counterstrike, etc) but are STILL fairly niche on consoles (outside of halo and other FPS on x-box, are there any other big online console games?)
That's not to say that online gaming won't have its place, just that its not as important as some people seam to think it is.
