As a first time puppy purchaser, I think it would have bothered us a little given the quantity of literature stressing meeting one or both parents. I think it would also depend on the circumstances and general feel as well. If we got to meet Mum for a bit and had time to interact with her and then the breeder gave a sensible explanation for putting her away whilst playing with the pups, then I'd be less put off.
As it was, our pup's Mum hasn't been excessively fussed with the puppies either time we visited. She'd pop in and out to feed or clean them, but what she really wanted was our attention And, as a result, my younger brother has ended up falling more in love with her than any of the puppies ;)