Yes. They want to keep people from burning through the content too fast, so that they don't get bored and quit.
Saying you can just roll an alt once you've burned through the content on your main is getting harder to stomach, since you have to decide whether you're going to enjoy just leveling the alt - or taking it all the way to 90. [I have a main and two alts at 90, and three alts at 87/88].
Have you played any MMOs that went F2P? I played Aion for awhile, before and after it went F2P... and it wasn't pretty. e.g. vanity skins for armor & weapons - especially holiday-themed ones - in the cash shop even before F2P, and then F2P brought time-stamped mounts, pack-pets, and furnishings for player housing. [yuck!]
Yes, they were actually selling items for in-game use which would expire after 10-days, or 30-days, etc. The mind boggles, it is so different from what I'm used to.
And, for me, biggest problem with Aion was crafting, which could fail - causing you to lose the mats you'd used for the crafting attempt. But don't worry! You can buy crafting "supplements" which will reduce/eliminate the possibility of crafting failing... as long as you are okay with the cost of those supplements sky-rocketing as the "iLevel" of the item you're trying to craft increases.
I can't imagine what kind of cash shop Blizzard would need to implement to make-up for dropping 15-USD [or equivalent] a month from a few million people. The mind boggles at the volume of sales they would need to make-up for the loss of subs - if the subs are still above a couple million.