It is true that there are some differences in pets / minions. However, every time I have a request to buff pets it has always been might that was requested. Kings may be another viable option, but I am not sure how it affects stuff like crit %, etc. There are a few mana oriented pets but I have yet to have to buff them.
In one raid where I was consciously trying to buff pets, I ended up using 100+ symbols whereas before I would use 50-60. And, pallies cried for a longer buff time because we don't want to be buffing every 5 minutes.
What it comes down to for me is that if I remember, I will give them a cheap buff and it may not happen again until we move to a boss. So, if Blizz wants to make pet buffing practical, they will look at some mechanic to make it so.