@glitter bomb, To me, "industrial" has always meant an actual industrial machine - used in an industrial setting typically for workshop or production work.
For instance, these are Brother's industrial machines : http://www.brother-usa.com/IndustSew...uctType=Sewing
My main "problem" with them when it comes to home use is that they're built with a very different audience in mind. They're invariably built for speed
- which may be unnecessary and frustrating, especially to a new user not yet familiar with the type of machine.
The teaching machines my college used were nearly $1,000 straight-stitch only machines, but they're listed in the "home sewing" category. They were very hardy and had a lot of "punch", similar to that of the 15-91.
The vintage industrials tend to be the HUGE ones - vintage Singer walking foot had an enormous table. The modern ones were about the same table-size as vintage domestic, but were still pretty heavy.
My personal recommendation, though, is to buy the cheapest machine you can find - buy one used, doesn't matter if it's the best machine or not. A really cheap machine will let you see how you use the machine - so if you realise you need something sturdier or more specialised, you know what direction to go. You'll learn what features are important to you and which you think your next machine should improve on. And if you take decent care of the machine, you can sell it to someone else and not lose much money.