What you say is not true for professional photographers or designers. For one thing, pro-level printers are in fact better than what the drug store has, which are optimized for speed, economy, and vibrancy — none of which are major concerns for professionals. They want accuracy and quality above all else.

For another thing, being able to print proofs in your own office is important. Having to run to the drug store to check color output is an awful pain.

Lastly, professional photo printers are often larger than what a drug store has, or at least higher quality at that large size.