I don't know that I disagree with the LHBS advice, actually. I mean, no real harm will come to a beer after an extended primary, but I often can tell the difference in a long primary vs a shorter primary due to the amount of yeast character imparted. The thing is, some people prefer that flavor. I do not. I read an experiment done by Basic Brewing Radio (didn't listen to the podcast) that had the same results- a percentage of brewers preferred the longer primary, and a percentage preferred the shorter primary.
Note- even the "shorter primary" was not short- it was like 10 days I believe! I rarely keep a beer in primary more than that, at least not on purpose. Normally 10 days is my time, give or take a few days.
I think that many homebrewing mantras have validity, so I would never dismiss someone else's experiences. I think the key is that the brewer is totally satisfied with their beer. If they are, then they should keep doing what they are doing.
I've had some absolutely terrible beer in competitions, and in beer exchanges here on the forum. TERRIBLE. But the brewers liked them just fine. I call that "UBS"- Ugly Baby Syndrome.
You know, those parents that have really hideous babies, but think they are the most beautiful children ever? Well, sometimes the same is true of homebrew. The brewer loves the beer because they made it. But when it scores poorly in competition, they feel hurt and upset because they think it's great. I think if a brewer thinks their beer is awesome, then they should not worry what other people think and keep brewing exactly as they have been.
A few years ago, I did a beerswap with another guy on the forum. The beer was not very good, and in fact was pretty bad. I couldn't really get it down. He asked me what I thought. I simply said, "Well, I like the clarity alot. But it's got a very strong harsh astringency in the finish". And he said, "Oh, yeah. I know. but how did you like it?"
Anyway, I didn't mean to take this off topic! I just wanted to point out that different techniques work for different people. But in defense of the LHBS guys, if they told me to allow the beer to stay in primary for a month, I'd think they were nuts! Sure, people have done it. And the beer turned out. But it's not really "standard" advice. There are some issues that could arise, due to headspace and such. For a chronic bucket-opening, it could lead to some infection risks. They could say, "Well, 10-14 days in the fermenter is probably the path of least risk. But some people go longer, and some go shorter." And that wouldn't have been a very good answer, although it's true.
So sometimes I"m sure they have to give a condensed "best" answer.