Happened to us. Found a great name for our bootstrapped product. The .com-domain was already snatched from a re-seller. They wanted 28.000 USD for it. So we went with .io like so many other tech products before.
If a layperson heard "visit us on the web at foo.io !" On the radio / TV, I think many would either search "foo.io" or "foo", or try foo.io.com , then get frustrated that it wasn't what they expected.