It _is_ dumb to limit access to just the price information and checkout/purchase page based on browser type. That being said...
If the customers don't care about the W3C, they won't care about having to download another browser either.
The combination of professional and elitist ("clientele for whom ego and image are everything") has a good chance of meaning they are either going to _already_ be using one of the listed browsers _or_ will want to find out how to enter the exclusive club they are not a part of. Thankfully, a link has been provided.
Looks good, works on all browsers, is cheap (in time and money) to implement. Choose two. Someone else just decided their priorities are different than yours.
I'd like to see some places start to put claims like "You're still using Internet Explorer, which has increased our development costs Nx over other more standards compliant browsers. This is one of the reasons our products are so expensive."