Correct - if Steem appreciates faster than user growth, there will be no problem and as demonstrated by Ether, even coins without a fixed supply cap can go sky high.

Though there really is a problem right now, when I wrote this post yesterday, I hadn't seen this chart from @elyaque:

I didn't think HF19 had an effect on the rewards pool, but it is quite obviously being drained faster than it is being replenished. Check out his post for more