I have to agree with the original poster on this issue.
I love Arby's, but most of the reason is because I LOVE Arby's Sauce and Horsey Sauce. I know it's unhealthy, disgusting to look at, and messy, but if my Arby's sandwich isn't oozing gobs of sauce, it just doesn't taste right. In fact, I don't think the roast beef tastes very good at all without the sauce.
In other words, I think Arby's roast beef sandwiches are a unique product. They are different from hot dogs, hamburgers, and fish. If I want a cheap hamburger or fish filet, I go to McD's or BK or half a zillion other places. If I want a cheap roast beef sandwich smothered in Arby's and Horsey Sauce, my only choice is Arby's.
So if Arby's (or at least the only Arby's in my area) were to "change" the taste of their sandwich (by limiting sauce) and make it less appealing, I would be less inclined to buy one (or two or three or five for $5). In fact, I probably would quit buying Arby's at all.
On the other hand, if Arby's raised it's sandwich price slightly ($0.05) and gave me 2-3 packets of Arby's sauce and 2 packets of Horsey Sauce per sandwich, I'd be a happy clam.
Anyway, my point is that, at least for me, Arby's has a niche market and can charge more to cover the cost of extra sauce.
So, yeah, charge a little more, keep the customer happy, and retain the same profit margin.
BTW, did I mention that I LOVE Arby's Sauce and Horsey Sauce?
Geez, I'm hungry now.