This wouldn't be a problem if people didn't abuse of it. Personally, it doesn't bother me, but I also don't see the point of saying it constantly over and over again.
I don't know if it's because that person want attention, interactions, or because it's really "agradable/funny”, quite questionable.
Regarding the comments that I have read that “welcome to the forums, happy birthday, etc” are the same as “pfp changed”.
- The “welcome to the forums” thing is done only once when a person joins to the forums, not constantly day after day in the same profile.
- Neither the "happy birthday" thing, since its done on a certain date once a year for each person, not constantly day after day.
I agree that maybe no one cares about both but its still something different that is not done day after day, they are not comparable things.
Therefore, it makes no sense to compare them with each other.