You know who you are:
You're building a mobile web app, but you're only supporting iOS and Android. Neither of which are exactly "web friendly" (I'm especially looking at you, iOS).
You're making a hybrid app with PhoneGap, but you're only using the iOS or Android build options. Because, well... because.
You see things with amazing mobile HTML5 support like BlackBerry 10, Tizen and FireFox OS and say "well, if they ever get more marketshare, we'll spend some time supporting them".
You're the "chicken" in the "chicken and egg" problem
Stick with me, this analogy holds. You know how developers like to wait for a platform to gain marketshare before they spend time supporting it? Well, that means less apps and compatible websites will launch on that platform. Less apps and websites means less curb appeal for consumers. Less consumers means... less marketshare.
By chickening out, you're helping to ensure market dominance of either a not-quite open source Java-based OS, or a walled garden "we only like HTML5 a little bit more than Flash" OS. Neither exactly embody the spirit that made the web great.
The reality of mobile HTML5 support
I like html5test.com. They score and rank browsers and mobile platforms for HTML5 feature support. It's pretty inclusive of all the goodies you could want with a possible score of 500. Here's the list today for mobile:
|Opera Mobile 16||471|
|Firefox Mobile 25||462|
|Windows Phone 8||332|
(* upcoming release)
Android and iOS aren't exactly dominating. Further, they're both playing catch-up with these smaller mobile OS platforms.
Yes, Windows Phone 8 is slacking (332), but not much more than iOS6 (387) and still worlds better than Android 4.0 (283). At least it's in the running, and not too far behind what a lot of you have in your pocket (iOS7).
Help shape the world
You got into software development because, let's face it: we developers run this stuff. The whole world depends on great software, awesome websites and sweet apps. Everything that has a plug or a battery these days has a computer in it (or will soon).
By choosing which platforms you support based on which are more aligned with your world (the web), you are helping to bolster the market appeal for those platforms. Ultimately, as consumers flock to consume your work on these platforms, you're making the mobile world more webby.
Think of supporting these other platforms as voting with your time
By porting your PhoneGap app over to BlackBerry 10 or Tizen, you're saying "I want a world with better support for web apps". By taking a little extra time to test your mobile website on FireFox OS or the Dolphin Engine (whatever that is), you're saying "I'm tired of spending a ton of time supporting an OS which likes to fiddle with standards so often it makes me cry" (again, looking at you, iOS).
If nothing else: why not help create a market with more choices? Competition drives innovation, and innovation means more toys for us web developers to play with.
There's really not much of an excuse
Given the megatons of open source cross-platform HTML5 libraries either for making apps or mobile websites, the burden of porting is minimal. Yes, there is always a testing cost for each platform you support, but that should be a small fraction of your original spend in supporting iOS and Android.
Disclosure: I wrote a cross-platform HTML5 app framework; one of about 5 million that are freely available today as open source.
So which came first, the chicken or the egg?
My money is on the chicken, every time.