Here are a few facts, from somebody who works for Honda (me):
All the Honda lawnmowers sold in the USA come from one place, and that's the Honda factory in Swepsonville, North Carolina.
There are no differences between models shipped to independent stores vs. those shipped to Home Depots; they are all the same.
Most independent stores offer all Honda models, but Home Depot typically only stocks the top selling ones. Home Depot can special order any Honda mower.
Home Depot and independent dealers pay the same price to Honda when buying mowers. What they actually sell them for is totally up to them.
The warranty provided with every Honda mower is valid at any authorized Honda location, including Home Depots and independent shops. It does not matter where you bought it, you can get warranty service done at any location.
When you buy from an independent dealer, they typically will have the mower fully assembled, fuel and oil added, and tested before you get it. At Home Depot, you can buy a mower still-in-the-box and get it prepped yourself (not hard, not tools required).
-Robert@Honda
Caveat: I work for Honda, but the preceding was my opinion alone.