We use PhoneGap's Media API to play audio when you export to PhoneGap, but it appears to simply not work. I have no idea why not. I'll have a look in to fixing it for the next build but I was disappointed with the results and heard it had other problems anyway from other PhoneGap developers.
PhoneGap's priorities currently seem to be around apps and not games so I'm not sure if they're going to fix game-related issues any time soon. Some PhoneGap plugins exist that can help, but PhoneGap Build doesn't support plugins yet. Without PhoneGap Build you have to download hundreds of megabytes of development software and go through a really complicated setup process, so PhoneGap Build really is the only way to go IMO.
I haven't got a great deal of experience using AppMobi myself, so I can't comment much, but I did seem to get Space Blaster working OK on my iPad via AppMobi so I'm not sure what "no tablet support" really means. IMO if it works use it, and I'd be interested to know how it goes for you.