From treadmill ratings and review website:
"Epic Treadmills are built by Icon Fitness, which is the largest fitness equipment manufacturer in the world. They also build ProForm,
NordicTrack, Reebok, Weslo and Image.
Icon Fitness not only is the biggest seller of fitness equipment, but they significantly surpass the next runner up. Due to the economy of scale, Icon can offer treadmills at a good value.
Their Epic treadmills have become a hot commodity, especially after they received a
"Best Buy" from a prominent consumer rating magazine for both 2008 and 2009. This has had a significant impact on sales."
As for what commercial companies (gyms) are buying, I don't know, although I do see these brands, especially NordicTrac, in commercial settings (anecdotal). The motor is a commercial grade motor with a lifetime warranty. I guess it depends on what you mean by "commercial grade". I use my Reebok branded treadmill about 5 hrs a week running anywhere from 30 minutes to two hours at a time and have had zero issues with it. Probably not the same as Lifetime Fitness where theirs get that much in an afternoon. Manufacturer warrants parts and labor (minus motor and frame which are lifetime) for 1 year, Costco adds a year, Amex adds another year for a total of three. My previous Icon treadmill (NordicTrac) worked great for over two years with no issues until I crossed a cable when I was reconnecting it after moving.
Check out the review site, it offers a lot of info on these brands and others as well as recommended treadmills.