My question is more theoretical than practial. I want to understand idea behind OpenGL API design in LWJGL.
For example in Android OpenGL API each following OpenGL API version just extends previous, I mean: android.opengl.GLES30 extends android.opengl.GLES20 android.opengl.GLES31 extends android.opengl.GLES30 etc
You can see source code here: http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.1.1_r1/android/opengl/GLES20.java, http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.1.1_r1/android/opengl/GLES30.java, http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.1.1_r1/android/opengl/GLES31.java
Why in Lwjgl there is no such concept? What is the reason behind such design when I have to use GL11.glDrawElements(); instead of GL43.glDrawElements(); ?
It's a choice they made with LWJGL. Submission of indexed geometry has been around since OpenGL 1.1 and they make it a habit of exposing what was added in later revisions, instead of giving you a cumulative set of entry points, as is common with extension loaders like GLEW.
It doesn't have to be like this (clearly, Google went down a different path and so did others, independent of the programming language) but in the end, it doesn't matter. All that matters is that the entry point is exposed to you. Sometimes it's good to see (and to know) at which point in time a particular API was promoted to core, but dividing stuff up like this can be quite cumbersome for the developer.
If it were defined in another way in the language of your choice and provided that this language supports interfacing with native code, the function you'd be ultimately calling would still be the same, because under the hood, the corresponding function pointer is retrieved with some form of GetProcAddress (depending on the platform, YMMV) and would refer to the same C function defined by the ICD (unless you link directly against an OpenGL implementation, in which case you resolution of function names would either be unnecessary when linking statically, or handled automatically during program load).