If you try on boots in a shop and they fit you really should buy them there. If enough people use the local shop as a fitting room then purchase online you'll end up without a local shop.
I agree, especially after seeing a handful of shops close up in my area. By no means am I saying that online shopping is the main cause, but it certainly doesn't help.
Building a relationship with local vendors also really helps if you have issues with anything you buy. For example, I run a freelance photography business and my $5k camera broke. The circuit board got completely fried and the charge was going to be about $500 to replace it. Since I got it second hand, there technically was no warranty. Well, I handed it over to my local vendor who I bought it from, they shipped it to Nikon, and talked them into putting a brand new circuit board free of charge. In the mean time, they gave me a loaner camera and didn't charge me a dime.