...or, it's just the natural result of friction to skin after having not bowled for 25 years.
Earlier this year I was practicing 20 plus games per week in addition to my three leagues. After Christmas I all but stopped practicing, went out last week and shot 14 games...result: a huge blister on the pad of my middle finger (exactly where it should be).
If your equipment feels good just give the blister a few days to heal and go at it again. Once your skin toughens up the blistering should stop. If it doesn't, then yes, you have a pitch and/or span problem and need to do some tweaking.