I think the reason he threw it out to the straight guys is summed up in Floridaswimmer's post about, "Girls seem to love the boxerbriefs".
Any guy that gets a coin flip, or best of 3, on being gay or straight that night gets an automatic free pass from women for wearing whatever kind of underwear he wants to wear, guys that they think of as "straight", well. . .I have caught my fair share of flack from women because of my choices in underwear.
Some nights I wear bikini briefs because everything needs to be held together, others silk boxers with chili peppers and "Hot" printed on them. Then again I weighed in for wrestling in front of 50 guys wearing purple bikini briefs on a $5 bet and it didn't make me gay, I don't think.
The point is, the straighter guys out there, who may only wear one thing would like to know what the ladies will tolerate (especially the first time before you have proven that what matters is in the package). Then he can skip the defense of his choice of underwear that night and not overcomplicate something that is complicated enough already.
As luck would have it, women and gay guys dig boxer briefs. I feel like they make me look like Milli Vanilli's albino stunt double, but to each their own.