Disagree.
People, like me, fill up their 32gb.
People, like me, have to juggle when they buy a new game (I just bought Muramasa; it's 450mb and I can't easily fit it. I have to wait until I finish P4G so I can claim 3.1gb back.)
People, like me, are more likely to buy the games they're thinking about if they can fit them on their memory card without juggling. I haven't bought Dragon's Crown yet simply because I don't have a 1gb to spare.
People, like me, get pissed off when they have to delete a game like SFxT as if we don't take the ridiculously slow backup method, we'll be downloading 180 different DLC items individually because the download list sucks.
People, like me, refuse to spend another $xxx.xx on a second 32gb memory card and juggle cards... I went full digital for the convenience... and when I had a ton of games I wasn't playing on my card, deleting things to make space (once I ran out) was easy. Now it's not. I delete everything I haven't been playing or have finished and won't be going back to any time soon immediately. And I have 480mb left and can't install the miniscule Muramasa.
So... while it's not necessary for you and people who think/feel the same as you, for people like me, we're going to be happy and more likely to purchase things if we have a larger memory card to use.
And the answer to the Steam question is "you install another hard drive."