Technically a B-wing is a large size ship and not a normal $20 small ship that the discount is suppost to apply to so you really shouldn't get the discount. I really don't think most places will go for that unless they just want to get rid of you. But heck if you can argue well enough you could get a large wing TIE for 40% off instead of $39.99. I wonder if they would give you the 40% off on a BMF.
The ad was a bit ambigious in that while it said
"40% OFF ALL Star Wars Battle Packs & Starfighter Vehicles
Sale 14.99 ea."
it did state that "ALL Star Wars ... Starfighter Vehicles.." (TRU caps not mine) and since the B-Wing was labelled a fighter, it was reasonable to include it in the 40% off (from my perspective). You're right though. I think it did come down to the person at the counter. I was polite to her, my two year old was charming, so I think she was willing to make a reasonable exception to how the computer wanted to process the sale. I agree the intent of the sale was for the ships we consider in the "$20" line (TRU sells them for something like $22, right?). But i think the wording of the add was such that the woman could reasonably make an exception.
So the moral of my story is that if you want to bend Toy R Us' sale a bit, give it a try, just find the most Grandmotherly looking clerk, bring along a smiling toddler and give it a try. Otherwise if you work for Toys R Us or their lawyer, I didn't do this, it was a guy I know.