I will try try to answer the question about restrictions of B fares. In some cases there are real restrictions: I have used non-refundable B fares to LHR. But the main restriction is that for rerouting. With Y fare you can change to *any* applicable flight with open economy class seats. With B fare you need B class to be open which may not be the case even if they are selling economy on the flight. This is meant to be main restriction, though it very rarely works as such in practice.

As to the price being equal, I am not sure. Here are a few samples:

BOS-SFO:
BUA UA B One-Way 899.00 (USD)
YUA UA Y One-Way 1049.00 (USD)

ORD-BZN:
BUA UA B One-Way 659.00 (USD)
YUA UA Y One-Way 933.00 (USD)

BOS-LHR:
B12E UA B One-Way 847.00 (USD)
Y UA Y One-Way 1463.00 (USD)
YCE UA Y One-Way 1488.00 (USD)

NYC-FRA:
BEE UA B Round-Trip 2677.00 (USD)
Y UA Y One-Way 2211.00 (USD) (4422 Roundtrip!)