Portability of Java-like virtual machines vs C native apps?

Hi,

I'm not familiar with Java or C and I need some clarification. I've asked before why did Android go with using a jave-like virtual machine on top of the linux kernel for Android phones instead of using native linux apps for Android phones?

One of the answers I got is portability. What I got is that for multiple hardware vendors, who will be releasing new and multiple hardware every year, apps made using jave-like virtual machines are more portable than native linux apps, because the later need to be recompiled for every hardware. Can someone expand on this for a beginner like me? Aren't compilers and interpreters supposed to form an abstraction layer between programmers and specific platforms? I don't get the thing about linux native apps being less portable.

Here is my previous question to Linux people.