Edit: Not saying that's always correct, but there does seem to be a tension between: "make sure your code can work well, even in a bad environment" and "don't mask bugs, instead fix them where it makes the most sense to do so" (in this case: in the dozens of browsers instead of in millions of websites).
Finding workarounds for browser bugs is a common theme for the work that web developers do. Yes, browser vendors should fix the bugs, but in the meantime, there's no reason to have a bad user experience.
If a mechanism exists to prevent your customer from perceiving this, as a business the smart decision is going to be to use it.
"i'm getting a lot of corrupt unsupported browser when accessing video on other sites, so i'm using chrome. i can't figure out if it's flash or firefox but i'm tired of opening the hood, i'm done with FF for now"
Most of them looked for a workaround and spoofed the user agent, but they are the kind of people that fiddle with settings. Normal users probably either don't notice or change browser.