You can call it a style if that makes a difference. I think there are reasons behind that style, and I think the too minimal standard library is the main reason. The lack of a good package manager until recently may be another contributing reason.
I hesitate to answer your hyperbole about ten variants of equal signs. It's not uncommon for languages to have two notions of equality like ocaml has (or even more): Here's Python for example:
http://stackoverflow.com/questions/132988/is-there-a-differe...
To answer your original question of why anyone would prefer to not use startswith: I don't think anyone does.
I hesitate to answer your hyperbole about ten variants of equal signs. It's not uncommon for languages to have two notions of equality like ocaml has (or even more): Here's Python for example: http://stackoverflow.com/questions/132988/is-there-a-differe...
To answer your original question of why anyone would prefer to not use startswith: I don't think anyone does.