I don't think there's a stigma attached at all, but that's just my perception.  I mean, does anyone think men don't masturbate as often as women?  
 
To me, the biggest difference has been in the lagging technology - women have had penis substitutes forever, but it took until just a few years ago to come up with a product that closely resembles the feel of a vagina.  And yes, I'm speaking from experience - I bought a Fleshlight a few years ago.  I no longer have it, because I thought the preparation time and the cleaning up time afterward outweighed the experience itself.  But it's a very awesome experience for anyone who's been disappointed and felt ripped-off by inferior products in the past - and I'll admit to occasionally regretting throwing it away.
Genuinegirly - great point about men and women 
both being able to enjoy vibrators.
But I think we can give the people at Fleshlight a pass on disguising it as a flashlight or large can of beer.  I mean, it's not like you display your dildos on your coffee table, right?
Besides - it's actually a case (literally) of form following function.  The "action" end of the product includes the fake outside genitalia, and therefore needs to be a larger diameter than the rest of the tube.  I don't think they originally set out to design something that looked like a flashlight; more likely the product got its name after the final prototype was produced.