Unlimited linking probably doesn't include embedding.
So, if they were on a lower end plan, something that used to be offered was taken away. After they invested time in uploading and embedding lots of images.
We're talking about 1 dollar per day for image hosting here. These panicky reactions seem totally overblown to me. I don't think this is really about the price as an absolute number. This is more of an emotional reaction about the price changing, which some people feel is fundamentally unfair.
In any case, how most photobucket users feel about it will ultimately matter more than what we outside observers think.
Also, that's just for one image hoster. If it catches on, a person who used a few over the years would have to pay thousands per year to avoid losing links.
But you're right that's not just about the money.
Especially considering nearly everything has a monthly fee attached these days.
$3 here, $5 there, $9.99 over there. Of course businesses should be paid for the services they offer, but as a consumer those numbers add up quickly, and in that context a subscription in the $30/$40 range is non-trivial, even for someone with a first world salary.
I can't imagine they provide that level of value, but that's just my opinion.
PG notoriously has stated a number of times that you don't need to even think about revenue, much less income -- just get users. You can do the switch later, whether it's blanketing with ads (see imgur), subscription plans, etc.