Gartner's report is in for the Q1 quarter of this year, and it seems Android saw a substantial growth from a year go, rising from 57% to almost 75% of the market for smartphones sold in the quarter. But can Android repeat this growth a year or from, or will it stop here?
I've always believed Android could reach over 70% of the smartphone market, because it was an open source OS with a lot of momentum that virtually every smartphone manufacturer is using, with a few exceptions. So for that reason alone, it should at least get close to the market share Windows had in PC's.
The difference is that historically the smartphone market has been very fragmented, and pretty much everyone wanted to use its own proprietary OS, and the fact that so many are now united under Android is a big enough miracle. But at least one company, Apple, managed to get a significant market share in smartphones with its own OS, and that's mainly because it started the whole "touchscreen smartphone revolution", and then managed to keep growing by having a strong app ecosystem that was significantly ahead of its competitors, at least until recently.
So Apple will keep holding part of the market, while other more niche operating systems with 0.5%-5% market share will take some of the rest. This is why I don't think Android can grow significantly bigger from here, but depending on how Android does in poor countries, and if Google makes Android even leaner for lower end devices, it could grow up to 80%-85%.
Unfortunately, each iteration of Android has been slower for low-end specs (I'm talking about sub-1 Ghz phones here), and I'm not exactly expecting it to get much leaner with Android 5.0, either, which should be released sometime this year. Hardware is getting ever faster, and the RAM and storage are getting cheaper. Google doesn't feel a whole lot of pressure to make Android run on even lower end devices, with new chips like Cortex A7 and Cortex A53 showing up for the lower ends of the market.
In terms of units being sold, there should be more and more Android devices being sold every day, because half of the phone market is still represented by regular feature phones, so there's room for the whole smartphone market to expand, and for Android to grow in terms of units sold, even if the market share number remains more or less stagnant in the future.