Yes, but keep in mind that, like BitTorrent, IPFS also includes a thing where nodes are given preferential treatment based on seed/leech ratio - so you're incentivized to help host content, and just the stuff you can share while downloading yourself might not be enough.

So yes, they will "unpin any site as soon as it becomes a resource drain" unless they're feeling particularly charitable - but that's exactly how it works with torrents, too! Generally you set up rules like "seed until a maximum up/down ratio is reached for that file, then don't bother", "restrict uploads to a certain maximum speed and/or certain maximum amount of data per day", that kind of thing. I figure you'd basically have an automatically-managed cache of limited size that you'd use to hold the stuff you were liking-to-pin, and stuff that was judged to be no longer worth seeding would get kicked off, as would old/unpopular content if the cache had filled up and you were shuffling in new content.

So unpinning anything that becomes a significant resource drain is also - at least in the relatively-short-to-medium-term - fully compatible with other people being willing to "like" your site to pin it, if not perpetually, than for an extended period of time.