The Husqvarnas are the same at the Big Box stores as they are at the dealers. Here is the difference: The Big Box stores generally has their machines assembled by stock clerks who probably know next-to-nothing about snowblowers, whereas the machines at the OPE dealer are assembled by someone who (hopefully) knows them inside and out. So, you can save a few hundred dollars by buying at the Big Box stores, then if you are mechanically inclined, you can re-assemble the machine, or you can wait until it breaks and then take it back to the Big Box store (oh wait, you can't do that, you have to take it to the OPE dealer that you shunned in the first place). Sometimes the machines won't even work when you get them home from the Big Box store, so you have to take them back anyway, then the Big Box store has to sell them even cheaper since they are "used" or "open box". More often, the machine from the Big Box stores works just OK, but not as well as it should because it wasn't adjusted properly, so the average user is quite frustrated with the machine but doesn't really know why.
Long story short, if you don't think you could re-build the machine yourself, save yourself a few hundred dollars worth of headaches and purchase from the OPE dealer.
Also, when you get to higher-end equipment, only the dealer carries the good stuff. For example, the Cub Cadet stuff at the Big Box stores is made by MTD and is relatively low quality. However, you can go to the Cub Cadet dealer and purchase a higher-end model that is still made to Cub Cadet's original high-quality standards. Same can be said for John Deere tractors. Cheap ones are available at both the dealer and the Big Box stores; however, only the dealer gets the good higher-end models.
Not much difference in the engines. A good B&S is better than a cheap Kohler and a good Kohler is better than a cheap B&S. Kawasaki is better than both, but also more expensive, which is why you don't find them at the Big Box stores. You get what you pay for. The cheaper engines are mfr'd. in China.