Depends on which "they" you're asking about.
Yes, Riot did make ARAM a matchmaker game pick. You can queue up for ARAM like you can normal, dominion, TT and ranked games.
No, not everyone made ARAM-specific accounts with only their favorite ARAM champs unlocked on the account to exploit in ARAM mode.
...but a lot of them did. And, since the matchmaker version of ARAM gives you rerolls, it's also easier to get the champs you really want than it was in custom games. You could argue this is why the custom games were dodged so often (which is true), but since I've seen matchmaker ARAM queues get dodged just as often anyway, it's a moot point.
Long story short, people are dicks. This isn't news.
Oh, addendum: I find it completely stupid that the matchmaker ARAM games don't let you see the enemy team's champions until seconds before the game starts. At least in customs you could see the team you were up against and plan accordingly. There's barely any time to make reaction mastery/rune/summoner spell changes if you need to (like if you see the enemy team has Mundo, Fiddlesticks and Vlad and would like to persuade your team to get at least a couple of ignites in place of barriers to deal with all the healing that's going to be going on, or more than one exhaust to deal with a team that has nasty jump-in assassins, etc.). The only nice thing about it is that you get more IP, but who the hell was playing ARAM for the IP in the first place?