Android version 2.3 - 2.3.2 (API 9) are declared as obsolete, and according to Android Market statistics, are very rare (0.5% of market users).
The question is: Why is API 9 declared obsolete and more importantly, is there any reason why should I not use it? I've been using API 9 and see no problems with it... am I missing something?
Better not fix it if it's not broken, right?
EDIT:
Clarification: If I would update my applications' API from 9 to 10, what would be the benefits?
I can only see negative effects: 1% of users will suddenly find out that the app doesn't work on their phones any longer. This is even worse with paid apps. Or that I'd be forced to maintain two versions of each app.
Have a look at the description of API levels. Gingerbread API (9) has been replaced by Gingerbread MR1 (10). You should upgrade to this API.
The current version of the android OS is 4.0 (Ice Cream Sandwich). 2.3/2.3.2 is quite a few versions ago and was quickly replaced by 2.3.3. (api lvl 10), so it is very reasonable (as time progresses and changes / updates are introduced) to "shelve" a specific version so to speak.
However, the one strength in the android OS is backwards compatibility. While older devices (pre 2.3) will not be able to run your applications, all applications going forward will. There is technically no problem running the older OS's but bug fixes/changes...etc mean you may be inadvertently using buggy code that contains security flaws or other issues.
It's best to pick the API version that will reach the majority of your target market most effectively.
For example, if you wanted to take advantage of some screaming new OpenGL features on the newer higher powered phone you wouldn't want to run it an older API level and possibly create a storm of angry users because their phone doesn't have the HP to run it!
However a more simple application might be fine just running on an older OS (like the Chuck Norris random fact generator).
You should always go for the lowest possible API to use. Simply because the lower your API level is, the more users can you reach.
So looking at the current stats, you are able to reach 97.9% if you "dumb" yourself down to API level 7.
But why API level 9 is obsolete? One could not know for sure, but most likely because it had some major flaws.
The Lvl9 is obsolete because if you want to develop for Gingerbread you should use 2.3.3+ (Lvl 10). This is because the "old Gingerbread" (lvl 9) has some significant issues.
Well, I don't really think you should be worry about the OS itself. But many Droid programers, like myself, are not testing Gingerbread version on emulators. Mostly, because it's not showing on the SDK interface (appears only when you check the obsolete filter). So, I guess that other programers are ignoring this version also. That's the only problem I can think.
来源：https://stackoverflow.com/questions/8353503/why-is-android-api-level-9-obsolete