Actually, becoming a Pokemon Master has nothing to do with the phrase "Gotta catch 'em all"....
That phrase was just a marketing thing used for the first season of the dub and they obviously got that catch phrase from the games.
And as for Ash wanting to become a Pokemon Master, yes, he still wants to achieve that goal. He made that perfectly clear at the end of "Me, Myself, and Time".
I think at this point, the writers just aren't focusing on Ash's goal in the anime. Though I believe that eventually, probably in the second to last season (or in the last season), they will have Ash become a Pokemon Master. Of course, the obvious reason why this hasn't happened yet is - when Ash becomes a Pokemon Master, that would probably mean the end of the show. ^^o
Anyway, becoming a Pokemon Master has nothing to do with catching *one* of every Pokemon there is, but rather it means: being the world's greatest Pokemon trainer.
So yeah, a Pokemon Master is just a title or rank, for being the world's greatest trainer.
This is just another mystery of the Pokemon anime. I mean, they've never defined that term before in the anime....
Also, it's kind of funny how we all know that Ash's number one goal is to become a Pokemon Master. But as viewers of the show, we don't know what one is yet - because they haven't revealed what a Pokemon Master is, or even the requirements of how someone can achieve that title/rank. All we know about the requirements for a Pokemon Master is what Ash does - going to every region, earning all the badges, and competing in that region's league.
But besides that, what else is required for Ash to achieve this goal? There has to be something more to it than that, and I'm guessing Ash might have to defeat one (or all) of one region's Elite Four members.