I think things are changing.
1. The marijuana community in general has become a lot more informed. There's a lot more science and a lot less hippie bullshit in the decrim/legalization/mmj movements.
2. Marijuana has been around long enough for most people to realize that it's not killing anybody. There are still those who use faulty reasoning to oppose it, but the reefer madness era seems to have passed. Even the gov't has realized anti-drug ads are more effective when you tell the truth about weed (it can make you lazy and boring) than when you demonize it with mis-information (accidentally shooting your friend).
3. A lot of it is just an age/generational thing. People who grew up around marijuana have a much more reasonable view of it than those don't have any experience with it. As time goes by, more young people are joining the electorate, and more old people are aging out of influence. (Similar to gay marriage -- statistically, the younger you are, the more likely you are to have no problem with it.)
4. The stupid "hippies vs. reactionaries" culture war from the 60's and 70's, which has defined much of the recent political landscape, is finally starting to wane. I have mis-givings about many of Obama's policies, but one thing I really do love is that it feels like he's the first President from the generation after Reagan/Clinton/Bush, and thus isn't as bogged down by the baggage of the last few decades of politics.
Like most major social issues, marijuana is only going to be legal when the majority of the population (rather than the powerful in government) want it to be. If we see its legal status softening, I think it will almost certainly be a result of state-wide initiatives, rather than a decree from the federal government.
