No sex in a bdsm scene is very dependent upon a) the players, and b) the location. If you are going to see a prodomme (as opposed to a provider who offers some of these services) then most likely the only sex that will be encountered is strap-on play. Some will allow the bottom to jack-off at the end, others won't. Most prodommes are very, very, very upfront that they are not prostitutes. And most don't like being compared to them, but say they are tolerant of what they do. An irony that sometimes I don't get...
Provider dommes seem to be far more willing to indulge in sex (duh!), but the ones I have met or talked to, well, I wouldn't put their bdsm skills at the same level as some of the prodommes I know. There is far more to the scene than getting an outfit at Hot Topic, some boots/heels at Electrique Boutique and your toys at the local adult bookstore. The really good prodommes have invested a lot of money in equipment, gear and outfits. Spending $300 - $500 on a corset is not unheard of, as well as getting good floggers ($100 or so ea), cuffs, inflatable gags, etc. Quality costs money. And then there is the small thing of actually knowing your craft. Being able to tie a bow-knot is not nearly enough when it comes to being able to use a rope to make a body harness, to suspend someone, etc. And to top it off the better ones can do all that PLUS fuck with the bottom's head - and do it all safely. It's certainly an investment in time and money to really get into the business and to stay there.
The other thing about sexual play is location. As was mentioned by others, penetration play is frowned upon or prohibited at public parties. Why? Because its an easy way to get arrested and have the venue shut down. It's a result of the local laws and ordanances. There are exceptions to the laws. For example, its illegal in a public place to fondle someone for pleasure... but it's quite legal to fondle them painfully. Our lovely legislature did not take into account pain = pleasure for some!
Now, you can also get around this by having a "private" party. These occur at places like SPLF, as well as Sanctuary, but they have to be labeled as such. And the tickets for them can't be purchased by walking up to the event. If they are purchased in advanced, and the party is labeled as private, it can be considered a private event, and therefore is not subject to the same public indecency laws. You can fuck and suck to your hearts content.
I know a lof of people have complained in the past about how Sanctuary limits the activities of people... but there isn't much else they can do if they want to remain open and as a community resource. We all know a little, ahem, 'cheating' occurs from time to time, much like what it does in the strip clubs. You just have to be careful and reasonable about those activities, and all is well. I much prefer having it around for a long time with the restrictions it has on it than to see it go away because someone can't keep their pants up (or skirt). There are alternatives and ways around the issue.