Just throwing my $0.02 as a web designer in here....
The days of "using browser detection" to limit access to websites came and went LONG AGO.
Some folks "just didn't get the memo".
Plain and simple, if you're visiting a site that won't allow other browsers (when MSIE only comprises about 14% [at best] of worldwide browser use anymore), that's a good sign that most everything at the site hasn't been updated in ages, or if it has, it was done by someone who hasn't used any new software since about 2003. These people are ingoring more than half the people who could visit their site, with iPhones, Firefox (#2), Chrome (#1), Opera (#3) and Safari (#4), not to mention Linux users who nearly ALL use Firefox and are now moving to Chrome too.
Frankly, anyone who "slams the door" on that large a percentage of their potential audience or business.... won't get my time for anything.