If my MS is shorter than 200,000 words I'm going to be very surprised.
I've rarely been satisfied with short books. 80,000 words seems ridiculous to me; I can't even fathom it. The Postman was really short, as I remember, and I felt like it hurt that novel a lot.
I'm not saying it can't happen, but in my experience, it usually doesn't. Or at the very least, the ones that have stuck with me have run on the longer side.
It's not really a bias, because I don't go looking for longer books. The best ones I've read just happen to be long.
Blade of Tyshalle, by Matthew Woodring Stover, is just about tied for first place as my favorite novel of all time, and it comes in at over 300,000 words. In fact, I think it's closer to 350,000 words.
While it's mostly true that the more space your book takes up the less books you'll be able to fit on the shelf, there are all sorts of font-size and spacing tricks publishers use to cut down or increase the amount of size in your book. Again, with The Postman, I've got a hardcover edition that I think runs like 175 pages and that thing looks damn near double spaced, with probably a 12-point font. Which means that in actuality, the book probably runs less than 100 pages, which is ridiculous.
On the other hand, with Blade of Tyshalle, it's single spaced for sure, with probably a 10-point, maybe even a 9-point font. It's really small, and it still runs 790 pages. But that's how they crammed it together in a nice sized package.
The softcover version of Scott Lynch's The Lies of Locke Lamora runs over 700 pages, but the font size and spacing is much more traditional. If I recall though that book ran close to 220,000 words. And TLoLL was Lynch's first book.
Quality writing sells. If somebody tells you to shorten your MS, it's the result of a lack of faith in your writing. Doesn't necessarily mean you shouldn't listen to an editor telling you to shorten your book, and as a first-time author, if somebody's offering you a book deal you might be crazy to turn it down rather than tighten things up. But ultimately, if you write a 300,000 page novel that kicks ass and takes names for every fuckin' word of it, you'll sell it, and you won't have to worry about shortening it.