Seems to me that in an effort to remove the stigma, encourage communication, and that over-used phrase, "raise awareness", the whole idea that "rape is really about power, not sex" is getting over done. It most absolutely is a crime of sexual gratification, and yes, there are elements of surprise, dominance, and power involved, however they only serve to enhance the perpetrator's sexual gratification.
If it were all about power and not sex, "rapists" would just beat people up, make them lick their boots, and say something denigrating about themselves before running off into the night.
As to the underwear, I'm neutral on the idea. If in the heat of the moment the rapist doesn't realize that the underwear is specifically designed to stop him, he may just get frustrated and leave. Or it could be useful in date or party rape where drugs (voluntary or involuntary) or alcohol are involved, and the rapist is more opportunistic isn't as likely to be angry and forceful.