There are many professionals, like real estate agents, for example, and various other let's say small or even somewhat larger businesses use free email providers for their contact information that they provide and use. Many of them are excellent at what they do--in fact can often be better than the various large corporate entities in their field--and judging them by their email address or even domain name would be rather pointless in that respect. It's not to say that people don't do that, but that by no means makes it any more meaningful or worthwhile.
Comparing garbage inside of people's cars to what they use for their email address is apples vs. oranges comparison at best--they might both be fruits and edible, but they are quite different. Taking real life and applying it to the digital doesn't really pan out.
As for the "norm" of the internet, I think we all know how poor of a standard that is be to apply to real life in pretty much most respects unfortunately.
In any case though, everyone can certainly have their own biases, as I mentioned before. This part of the discussion can go back and forth without any particular right answer since it's different for everyone (even if sometimes not for any realistic reasons). Don't want to take more away from the actual subject of the thread though on a side discussion.
You're saying you'd feel the same quality and perception of service from bobjohnsonrealty@yahoo.com as you'd get from bob@johnsonrealestate.com ? Wow, I think you stand alone in that one.