I guess people just have different images of the type of job they're applying for. When one of the local brewpubs lost the brewer a few years back (he moved) they put out a call for applications, no professional brewing experience necessary, they would hire homebrewers. I would certainly expect those applicants with no history to bring samples.
If I was the head brewer and a homebrewer was applying for the assistant brewer position (which is the bottom rung at most of the breweries in my area, if the head brewer is fortunate enough to even have an assistant) I would want to sample their beer and talk to them about their process, see if they could critically evaluate their own beer. You can tell if someone has at least some clue about sanitization if you taste their beer - if they bring you a sample that is clearly infected you know first, that they screwed up the process somewhere along the way, and second that they don't have a half decent palette if they are sharing this with anyone except as an example of what not to do or asking what went wrong.
Brewing can be taught, so can cleaning so I wouldn't require an applicant be a homebrewer or have experience brewing. You obviously want a hard worker and someone who takes pride in their work and wants to do the best they can. It also helps if they like beer and are interested in the process, and those types of people will probably have at least tried to brew at home. I think there are good reasons for bringing a sample, and if there are a slew of applicants it is something that can set one apart.
And Keith, just because I bring you a sample doesn't mean I expect you to brew it. Who says I'd even give you the recipe?
It also doesn't mean that I think my beer is better than yours, and if someone came in with that attitude then don't hire them (unless they're right, then maybe you should think about it). To me it's just about sharing a beer and a love of beer, and if a homebrewer doesn't want to share their beer then it seems to me it probably isn't very good and they're not interested in making it better.
But that's just me.