I find it a bit off.
I understand weddings, because my thoughts are people generally spend a bit (unless you are the majority of our closest friends who got nothing) & it does give people an idea of what to get - you don't want 20 serving platters or vases or cutlery sets etc.
Even baby showers make sense but I think most things I could have put on one of those would have been too high a price point (people would be better putting the $20 each on the registry for mother to buy something at the end).
But as Traveller I agree with Trav - "However for the engagement parties (with only a few items below $100) it just left a really bad taste in my mouth".

My questions - I have an engagement invite with a registry.
I wouldn't want spend more than $50 on an engagement gift unless it was someone super special (these ones are not).
So, etiquette-ly speaking - do I have to buy from the registry or not?
We have decided not to attend the party and I would still like to get a gift but I baulk at the cost of purchasing anything on the registry.