This is an interesting topic for many apps. There's exactly the same request for ArtRage, a graphics app that has a PC following and an iPad app, but no Android version yet, despite the Galaxy Note offering the best graphics tablet experience of any tablet at the moment.
The observation that Android devices are outselling iPad devices is misleading though. Firstly the number of devices is not as important to a developer as the amount of content sales, and I've heard that less software is bought off Android. I haven't a full source for that to quote though. Secondly though, Android hardware is made of lots of different devices meaning the same code doesn't always work across devices. My own app that I tested on an ASUS TF101 is bugged on my new Galaxy Note 10.1, despite using only official APIs.
In writing high performance software such as iPad has, you need to write what's called native code on the Android device, which means writing a different version of your program for each different flavour of Android device. That means one for Mali, one for Tegra, one for Snapdragon, and one for PowerVR, plus whatever other chipsets. If you want to know how bad that is, the new Samsung Galaxy S4 actually has two different chipsets depending on phone model bought. You could write native Snapdragon code that will work on some S4s and not others. Owners of the S4 will not know version they are getting and will only see some software not working on their phone but working on other S4's and being rightly annoyed, but that's hardly the developer's fault!
Android hardware diversity also means maintaining a suitable hardware test base and going through lots of QA; something like an order of magnitude more effort than developing for iOS.
I have to say that I regard my Note 10.1 as the best tablet computing device going. The stylus is superb. The accuracy of the point-perfect interface makes handwriting tiny writing (writing labels on images), or selecting small icons, as easy and intuitive as using a touch-screen with cocktail-stick sized fingers.

I also have a stylus with an 'eraser' on the back, meaning a flip of the pen changes input options. There's nothing quicker or more natural. The potential for music notation on this device is better than iPad because you can design the software as digital paper with the same degree of accuracy. You could handwrite notes onto a stave and have Notion turn them into digital versions, beautifully presented and played in MIDI. You could flip the pen and tap notes to open properties or erase them or move them or whatever. It'd be the quickest, most efficient system. So I'd be very enthusiastic about Notion on my Galaxy Note.
I've been promoting notion with my choirmaster too, who's still in the dark-ages with music and has messy sheets of scribbled parchment to work from. I rewrote our last score in Notion and she was gobsmacked at the quality and possibilities. As she hasn't got a tablet yet, it's okay for her to consider iPad. But that means I can't share content with my tablet, and as she has years of hand written experience, she'd be far more at home with a hand-written interface as I describe above than the 'select note length and place on stave' of typical notation editors (let's be honest, that's a bit like selecting a letter and then pasting them one at a time instead of just typing/writing out words

)
Sadly, the situation is chicken-and-egg. As long as iPad has the best software, it'll attract the custom, and as long as people are buying iPads, there's not much point in the costly port of apps to Android. One solution is to target a subset of devices, such as the Nexus devices which are very popular (Nexus 7 especially) and then if the app works on other devices, they're lucky.
So all in all, Android is wanted but it's not a straightforward choice, and those requesting Android versions need to understand why. It's not developers being lazy or stupid, missing out on easy sales. Developing for Android (and supporting it!) is a whole lot harder and more expensive than developing on iOS, and that's why many apps don't get ported. This leaves everyone with a dilemma - buy into the Apple ecosystem, thereby reducing the value of Android even further and reducing the likelihood of future software on Android, or buy into Android and accept the software's not going to be there for potentially ages.
Certainly though, the moment Notion works on my Note (or potentially any other notation editor), they'll have my custom!