We could have told you this would happen a year ago, but people are just getting it into their heads that UMD movies are failing. While they are fine for video games—who cares what the media looks like?—they're a horrible choice for movies. Movies, on the whole, are purchased once and played at home. Therefore, offering Spiderman on DVD and UMD is a silly idea. If I care that much about Spiderman, I'll rip my DVD and stick it onto my PSP in some other, non-legal manner. Otherwise, I suck it up and watch it while sitting quietly on my couch.
Walmart seems to be dumping the media entirely and shelf-space in other stores is getting considerably smaller. Then we discover that Universal and Paramount are stopping UMD production. Oh well.