I don't think this is an escalating ringtone feature -- I think it's a bug. Possibly it's just really poorly implemented, but I've used escalating volume on ringtones with CM before and compared to that, the volume inconsistencies here are far too sudden and inconsistent. For example, sometimes half my notification is quite (or possibly completely silent?) and sometimes the entire sound comes out at the desired volume.
It also does it for tone it makes when you change the volume (i.e. the first time you click vol up/down, the tone it makes is way too quite, then you have to change the volume a couple of more times to get it play at the correct volume). Hopefully this isn't something they designed on purpose, b/c if it is then that's just a terrible user experience (why would I want the preview of how loud I'm making the volume to come out at the wrong volume?)
After using my Moto X for almost a week, I'm starting to see what you're saying, but I'm not sure Motorola would see it as a bug. I've noticed more than once my phone will be sitting right in front of me, and while the screen flashes on for a notification, no sound follows it, even though my notification volume is clearly up. If I go back in and try running manual tests, the notification sound works fine. It's possible that my notification tone (I picked Tejat) is just so short, that the 1-2 seconds it plays for is enough to get lost entirely as part of that initial volume ramp up.
Also have the same issue as you with the initial press of the volume control rocker as well...this issue also seems to extend to any menus that involve picking a sound file to play (like picking a ring tone). Any initial file played will always have its first few seconds lost, and then all sounds will play fine afterwards. If you exit the selection menu and go back in, same thing happens.
My guess is that the initial time an app plays a sound, the first few seconds get lost...following that, it'll play it ok. If you exit the app, it seems like this behavior is reset...which could be where it feels like the volume is inconsistent. But this overall behavior does seem like a permanent escalating ringtone "feature".
