Cheers to Mouse - I agree with your post.
Let's remember that we are ONLY hearing one side of the story, and the poster's interpretation of what transpired in the LFS. Something tells me (and perhaps my perspective is different because I walk in the LFS owner's shoes) that the recommendation was made somewhat differently than the poster recalls it...
But I digress...
Yes, a sumpless tank is "doable", but let's compare apples with apples...
$250 for a RR tank (I'll assume for a moment that it's an All-Glass tank) is more than reasonable. A 75 g non-reef ready (standard) tank from AGA or even Perfecto (P is lower quality, IMO) wholesales for more than the $105 that the other store is selling for. Therefore it's logical to assume that the other store is either selling glass at a substantial loss, or more likely, the tank is another brand, and so you aren't comparing the same quality between two tanks.
"The Bitter Taste of Poor Quality Lasts Long After The Sweet Price is Forgotten"
This applies to anything. YES you can get the cheaper tank, and do it with hang on equipment - I maintain a variety of tanks, and deal with a nice 80 gallon reef that is hang-on. However, if the customer was starting from scratch, I'd recommend reef ready for a bunch of reasons. Ditto I just set up a 90 for a customer who had the tank already, and we fitted it with an overflow box and sump, but with overflow boxes come an increased flood risk, they are harder to keep clean, there are just so many reasons to go with a reef ready tank.
Perhaps the LFS owner's comments came from a concern that the hobbyist is only interested in cutting corners, and not providing proper care for the animals - Goodness knows I've "not sold" many things to many people - and I've kept them as happy customers because they know that I have their success and the animals' success in mind. A short term money grab on a creature sure to die, is not a good way to do business, but careful planning and good communication with the customer will assure his success and long-term loyalty.
Can you do it without a sump? Absolutely. However I'd be willing to bet that at some point, regret at not getting a reef-ready tank might set in. What's the hurry? Shop around, get the best price from all dealers in your area, for the tank you want - and do it right the first time.
Having been in the hobby for about 17 years now, I've got a rather hefty salvage box in the attic with stuff I've bought over the years, and most of it was cheap stuff that didn't cut it - and I spent plenty of good money after bad, to upgrade after the fact. I could have saved a bundle in reality, if I had done it right the first time.
And yes, it's really annoying for an LFS owner to answer questions for hours on end, just to have the customer buy online or elsewhere... but unfortunately that comes with the territory. Speaking for myself, it's what I do to help hobbyists with their systems, and most times the reward is from a happy customer. Sometimes it's an investment that rings somebody else's cash register, but if the livestock is healthy as a result of the exchange, then one has to take some satisfaction out of that, even if it doesn't pay the rent

Hopefully if the customer gained useful information he'll remember where he heard it when he's ready to make another purchase.
HTH
Jenn