Hmm, I'd guess that difference isn't significant for the vast majority of players. And for those that care, the greater depth of Threes is surely an advantage.

I think 2048 became more popular because it was a) on the web, and b) free, whereas Threes was only on the iPhone and cost a few bucks.

Oh, and c) the OP, to give him his due credit, did a really nice job with it! It had the same kind of simplicity and virality as Wordle.