Well for some schools, lots of those fields are required, meaning you can't actually submit the application without filling out the fields.
I totally get your frustration, but here's where I think 2 of them come from:
Mom's university: On top of wanting to know if you have any ties to the university, my guess is that understanding your family background may paint a more complete picture of you, although I agree that there are a lot of assumptions being made on their part if they will assume certain things are or aren't true based on where your parents went to school (other than whether they're an alum of the school you're applying to)
I don't know how many previous employers you have, but I don't think the schools necessarily need you to write every single summer internship you had going back to high school. I had several summer internships during college and 1 part-time job and I didn't include every single one on my applications, largely because there wasn't enough room, and because some of them were somewhat irrelevant to my career path, so i included the most recent summer internship, my part-time job, and all of the full-time, post-college jobs I've had. But in terms of including phone #/address, I bet that it's so a) if they felt they needed to check up on a particular job they have the info to do so and b) it makes people feel like they can't lie/embellish because the school now has the information to check up on them if they need to. I'm sure there are people out there who might try to lie.\
As for other schools applied to--only one school asked me this question, and at the time, I hadn't decided exactly which schools I was going to be applying to, so I left it blank (it wasn't a required field) and no one ever asked again.