The big issue for me isn't getting people to agree on an edition: it's finding people in the first place. Not just anyone, but someone who's willing to read the rules (at least partially) and, y'know, actually show up.
I've had trouble getting reliable people since I first started GMing. My first group had four players, one of whom would follow exactly the same pattern for every session after the first two or three. I'd announce the time of the next session to everyone several days in advance, and he'd say that time worked for him. The day before the session, I would check with him to make sure he was still coming; he would assure me that he was.
The day of the session? Nothing. No phone call or text to say he wasn't coming, and no answer when any of us tried calling him ourselves.
(I hope it doesn't seem like I'm ragging on this guy; he was fun to hang out with, very knowledgeable about D&D - particularly Forgotten Realms, since he read a lot of fantasy fiction - and overall a good person, but this was a pretty annoying habit he had.)
In my slightly nebulous group that started off playing AD&D 2nd Edition, I was able to get the group to meet a total of one time. This session was never finished; one of the players had a call from "work" (of dubious legality), and had to leave immediately. The others soon followed. The next attempted session, the only group member who showed up was the guy whose house we were playing at. Fortunately, he brought one of his friends, and even more fortunately, I had a pre-made character he could use. Unfortunately, that unexpected friend had to leave unexpectedly.
More recently, a B/X D&D game I attempted to run (one session so far...) collapsed in a perfect storm of unplanned delays and last-minute changes of plan. One of the players wasn't feeling well, one was still out of town visiting friends, one was tied up in some kind of legal matter - a disputed ticket, or something of that nature - and one just plain overslept after a late night. The one guy who did show up went with me to grab some video games for what turned out to be (in a kind of baleful synchronicity) a mini LAN party that failed due to a faulty cable. Considering the work I've put into this so far, I'm wondering if I should try to have another session with the same group.
Speaking of video games, that's probably why tabletop games seem to be played so little. In today's world of blogs, PDF stores and print-on-demand, a game can be made and distributed for minimal cost, and reach a far wider audience than one which would be subject to corporate marketing requirements (side note: I saw a gigantic hardcover copy of Dungeon Crawl Classics at one of my local chain bookstores). The problem is, no one wants to put forth the effort to play in one of these games.
I know I'll probably come across as a disgruntled cynic of twice my actual age, but I see no more obvious culprit for this than video games. A person can sit at home on their computer (or in front of their console of choice, etc.) and immerse themselves in a highly addictive, brightly colored fantasy world with thousands of other people from all over the globe... or they can try to get together with half a dozen real-world friends, have to read stuff - read, as in words in a book! - and roll dice for four hours.
A telling sign? The university I attend has a semi-official League of Legends "team", but nothing in the way of tabletop gaming. I'd wager that there was a group of avid (A)D&D players here ten to fifteen years ago, but no more.
At least another FLGS opened up recently that has table space for RPGs; of the other hobby/game stores in town, one caters mostly to R/C and Gunpla (and consequently has no tables, although they do have some Warhammer and The Hobbit wargame stuff), and the other doesn't allow RPGs to be played at their tables (only card/board/wargames). Every so often when I'm doing stuff there, someone walks by and asks what we're doing. Genuinely curious.
...Maybe I should ask around there soon.