This is a new area the HD is trying to get into. Starting in Georgia I believe. For other things they have sub-contractors do. Its something to do with customer support. Certain jobs you can respond back to HD (complaints etc say for window replacements) but other jobs (storm door application), they direct you back to the subcontractor. The guy said that they eventuially will do everything. Yeh, I have that quote and have another reputable company give me a quote today!
Will let you know an exact price comparison.
p.s. the HD replacement windows these guys put in are slightly better than what is in the stores and havee excellent lifetime guarantees etc. Pretty solid setup. I have also requested information about other "jobs" they have done in the area so I can see the workmanship etc.