At the end of the day, we're all just a bunch of kids banging their action figures together, wondering Who Would Win. I think execs have been aware of that draw for a long time, and gaming is just now entering that phase where the major publishers are really being established, each of them with their own legacy to show (like I said in my last post). It's just a part of being one of the younger mediums.
I normally hate crossovers unless the crossing over was justified in game (I.E. The King of Fighters in its entirety), or if the I Ps the characters come from are actually still active. There's nothing I hate more than knowing that Darkstalkers still has a lot of potential, only for a minute fraction of the characters from that universe to be whored out in games they're only costarring in. Smash Bros. on the other hand still have a majority of their properties active.
ALL CREATURE WILL DIE AND ALL THE THINGS WILL BE BROKEN. THAT'S THE LAW OF SAMURAI.