When we do our mapping missions, a lot of those are inside Bravos but we base in outlying Deltas or Charlies. When departing Charlie or Delta VFR, we are usually always told to avoid class Bravo. We then get on with approach and request a Bravo clearance in addition to what other info the controller may way in regards to our mission. When doing VFR approaches for recurrent, the IAF for a local RNAV is inside of the Bravo shelf by about a mile. We request that IAF and are granted. 90% of the time the controller does not give us "cleared into the Bravo" and we have to query ATC about it. They come back on in a voice sounding like "oops, I forgot that part" and clear us in. It's this way in many areas around the country. I would never enter Bravo VFR with out explicitly being told by ATC, "NXXXXX, you are cleared into the Bravo". As others have stated, it's a CYA thing.