The developers have always pointed to European board games as an influence on 4e design. Particularly anytime they were asked about MMORPGs' influence on the design, the response was, "Sure, we looked at everything, MMORPGs, board games, and card games."
What always gets me is, why is this considered so off-the-wall, non-common sense, and foolhardy? Innovation is good for the game, it's always been good for the game. It was innovation that led Gygax and Arneson to create D&D in the first place, innovation was behind the Greyhawk and Blackmoor supplements that created the core D&D we all know today. Innovation led to 3e, which was a huge success and brought many new players to the game.
2008 was a different world than 2000, much less 1989 or 1977. RPGs now faced competition from console games, MMORPGs, board games, card games, and heck, just the Internet. We can look back at 4e and say, "Well, they should have stuck with RPGs strengths," but we don't know if that would have been the road to further audience loss and marginalization. They may have had the right idea but wrong execution. Who knows how it might have turned out if the Digital Initiative had turned out like they planned. I fiddle around with the Virtual Table and think it is truly an innovative way to bring the strengths of role-playing to the Internet. What if it had been 3D, with customizable avatars straight from the character builder, as initially designed? When I think of 4e in that light, I marvel at the ingenuity. A simple, elegant game outside of combat, easily manipulable by DMs, and then a detailed combat engine to spice up those online games. Taking the best parts of roleplaying games and adding new ideas from all kinds of gaming, and bringing it to the new media. I think in the end, it didn't work. Marketing mistakes that drove players away, DDI being buggy driving players away, a Players Handbook that was not an easy entry into the game (and I like 4e), the GSL driving third party publishers back to the OGL. Plus the economy crapping out just as it was released. The game itself aside, a lot of things went wrong for 4e. And while I'm a fan, I can't say the game itself might not have been too much change, too soon. But, goddamn, WotC reached for the stars. They fell short, but I admire the effort.
The way I read Mearls' comments, all he's saying was they tried design 4e with cross-over appeal, so they could easily introduce board gamers, and video gamers to D&D. And what Castle Ravenloft taught them was that the RPG itself doesn't have to be the gateway. I don't think that's necessarily an obvious conclusion they could have come to in 2006/7 when they were designing 4e.