More or less the term professional means just that. But.....it also designates that it was made in Germany, rest are made in the US. Although that is changing as Stihl makes a greater presence in the US, factory (NJ I think). If you can afford any of the Stihls you are better off. I have more Stihls than I can shake a stick at, and all with no major problems.
My father is on his third cheapo chain saw, while still have my two Stihls. If you total up those three cheapos, plus the frustration, travel, time, etc, to replace them, I am sure that I am ahead.
Plus Stihls are actually supported by a network of dealers, something you do not see these days. My local dealer is excellent, and I have had equipment repaired there while I wait. Try that at HD. Most of the dealers are top notch, and Stihl proudly advertises this. They also advertise proudly that you will not find them in a big box store.
Long short of it, over the long run, you get what you pay for. At my local dealer, you often see 30 year old saws coming in for tune-ups.
Chris