There are many Mobile Devices available today. They are powered by Apple’s iOS, Google’s Android, Microsoft’s Windows 7.5 and many others.
In most cases App development is largely restricted to making apps on a single platform. But it is equally true that there are a lot of apps available across multiple platforms. This is true especially which firms that develop apps for their clients. Clients would ideally like to have their apps available across all kinds of devices. This helps them increase their reach with their consumers. This poses a lot of challenges to the developers.
HTML5 is a very common approach adopted by developers to solve the platform independence problem. A lot of people tell me that this helps solve the problem easily. Just make a mobile webpage using HTML5, embed a web component into your app & show the page on whichever device you wish. While this approach does save on development & maintenance time, it doesn’t really take advantage of the native features that each OS has to offer. Also if you are going down this approach it would be better off to just ask users to visit the website on a mobile browser itself.
Spending time making an app that uses native features of the OS is not at all a bad thing. It gives a great advantage of allowing you to improve the users experience & improving the performance of your app itself. Even if you have to make separate apps for each OS it gives a lot to the user, which should be the main goal of most companies wanting to sell apps.
For those users who are individuals making apps as a hobby or a source of income focusing on one OS initially helps a lot. As time goes on & you get more comfortable with the design & development lifecycle, you can start making apps for other OSes too.
Bottom line: Think about what your needs for now & the future are. If maintenance is really going to be a huge issue, then HTML5 might be OK. However, the best thing would be to make apps which take advantage of the native features of the OS.