I can see why someone would do it. If you are on Windows, you _can_ use other browsers - every browser is available on Windows.
When I allow an IE user to use an application, I have to start testing on IE. In order to do that I'll have to make Selenium do some extra runs (IE 7, 8, 9, 10, Metro mode) under a Windows VM. I also need at least one (Win 7) Windows licenses (probably more, but I may be able to get away with permanently using it in preview) and, worst of all, when it breaks, I'll have to get the application fixed for, at least a couple versions of Firefox, Chrome and IE. And that if it breaks during testing - if it breaks with a user I'll have to start guessing what went wrong (if something did).
Nah... Windows users can use Safari, Chrome or Firefox.
edit: as pointed out by recoiledsnake, aaronbrethorst and Impossible Safari is available for Windows.
I'm a Firefox user, working exclusively on Windows (although a Linux nut by night).
If a site blocks any browser by user-agent _and I find out about that_ (as a user of FF that's not a regular case) that site is dead. I will create some childish rhymes about the creator of that thing, I'm going to compare it to acoustic couplers or pay phones and .. move on.
There are good reasons to avoid supporting every browser and the IE brand _had_ (and has) problems.
But user agent sniffing? That results in one reaction only (again, of course, limited to 'what I can notice'):
This business isn't able to provide a usable web presence. I'm going elsewhere.
> This business isn't able to provide a usable web presence.
Define "usable". It's certainly usable if you are not on IE and, if the resources they'd use to support IE in addition to others are diverted into new and useful features, I'm happy.
Even if you use feature detection, you'll still have to test on IE (and, to do it right, you'1l have to test on a matrix of 3 or 4 OSs (XP, Vista, 7, 8) and 4 browser versions (7, 8, 9 and 10). If IE breaks, you'll still have to fix it in ways other browsers don't break. That costs money.
Anyways, the author's beef was not that IE should be supported at any cost, but the claim that the features needed are not supported in IE and that's why it needs to be banished by User Agent(complete with a broken IE icon display).
When I allow an IE user to use an application, I have to start testing on IE. In order to do that I'll have to make Selenium do some extra runs (IE 7, 8, 9, 10, Metro mode) under a Windows VM. I also need at least one (Win 7) Windows licenses (probably more, but I may be able to get away with permanently using it in preview) and, worst of all, when it breaks, I'll have to get the application fixed for, at least a couple versions of Firefox, Chrome and IE. And that if it breaks during testing - if it breaks with a user I'll have to start guessing what went wrong (if something did).
Nah... Windows users can use Safari, Chrome or Firefox.
edit: as pointed out by recoiledsnake, aaronbrethorst and Impossible Safari is available for Windows.