To some extent, yes, this is short sighted. Languages are all much of a muchness. A decade ago, Perl was the flavour of the month. All the hot new sites used it. Today the same niche is filled by Ruby, and Perl is something of a pariah amongst scripting languages (though still my first choice for anything that needs prototyping.) Whatever flavour of the month you happen to like today will inevitably describe the same arc. That's just the nature of the business.

The good news is that all these skills are transferable. Becoming a better Java programmer automatically makes you a better Python programmer, and vice versa.

What isn't transferable is domain knowledge. If you want to make something of yourself in this industry, you need to specialise in something. Learn everything there is to know about something, be it networking, writing compilers/virtual machines, security or operating system design, etc. If you don't, you're essentially doomed to a career of moving bytes from a to b, applying some trivial transform to them on the way. Which, incidentally, describes neatly the vast majority of web development.