Yes this is definitely a ploy by ann summers to aim at getting more sales. However i've always thought it was a silly rule as they are missing out half of the population that could be spending their hard earned money on toys etc, and a large majority of women that i know would not be put off my a male presence. As for a definitive answer, the sexual offences act 2003 does not state that it is illegal to have an orgy, as long as all the participants are of legal age and are willing.
I think it's time we had mixed parties and if they're not that enlightened how about all male parties as well. After all Ann Summers was a pioneer helping women realise that there is nothing shameful about embracing your sexuality. Perhaps it's now time to bridge the gender gap.
Hope that answers your question :0)