That's interesting. Currently I have 2 different domains at 2 different registrars. In each case I have the bare name, www and other subdomains as "A" records, not CNAME.

So it doesn't matter if people use the www prefix or not, since both point to the same IP. And with this configuration I've had no trouble with MX records.

If the goal is www/no-www transparency, there are other ways to do it, but using a simple DNS setup seems like the least hassle.