I look at it like this. I assume I'm giving away the $35 deposit (which isn't strictly true, because they take tolls out of it until you get to about $10, then bill for some more) in exchange for saved time. I've already saved at least an hour and probably more by using several interchanges which always suck frequently:
-New Stanton/PA Turnpike
-Philadelphia/PA Turnpike (the route 1 interchange)
-Cranberry/PA Turnpike (though this one won't matter much longer)
-Route 128 Toll Barrier/MassPike

I value my time such that an hour costs way more than $35, so I come out ahead. The only problem is now it doesn't cost anything to use toll highways in my head anymore, since I don't notice that I'm using the money;)

I understand why they did it. It doesn't require a large land footprint or any staffing whatsoever. The booths and the EZPass equipment were the only costs beyond the land for the accesses, which may have already been there (they seem to keep a lot around for getting e.g. emergency vehicles on and off the road).