For many people who play cRPGs, myself included, precisely for roleplaying reasons, using mercenary companions is flat-out not an acceptable option. We want a custom PC, but non-custom companions.
How well does that idea work with "I killed Wynne, WTF! I have no healers anymore, BioWare you're shit at designing games!" that hiring/creating mercenaries help fix?
Moving from Act 1 isn't the time you might lose a companion, the other cases will all be role-playing reasons/choices.
Firstly, the comparison doesn't hold because in DA losing Wynne or any other individual companion does not close off any important skill areas for you because there are other companions available with the ability to cover you and also because in DA the "classes" are essentially superficial and you can add any skill (ex. healing) to any of your characters.
Back to the main point, yes, exactly, we stand to potentially lose some of our companions in later parts of the game due to the dialogue choices and other roleplaying decisions we make, not to mention them getting chunked. And if at that point my only option is to bring in an empty-suit "no interactions" merc, there is no way in hell that is happening. So I would either have to continue on with an even smaller party (and I consider four to be way too small a party size, so ...) or else restart my game from the end of Act 1. All rotten and ridiculous options.
