Why Ubuntu doesn’t support certain form of shebang for Python?

[vova]

PEP 394 and 397 suggest a simplified form `#!python2` — it works on Windows 
7 and 8 just fine.

But Ubuntu 14.04 claims ‘no such file’, though python2 is in PATH.
I googled that issue and found only similar issue with DOS line endings, but 
I’m sure that mine script contains Unix ones.

So I guess that form of shebang isn’t supported, which is unfortunate since 
it questions portability of programs written in Python.