യ ര ല വ

I read somewhere that there is no pure Tamil word starting with യ. Yes, there are words like യവം, യക്ഷി, etc. but they are all "obviously Sanskrit".

I read somewhere else that there is no pure Tamil word starting with ര! Now this might come as a surprise especially given the tons of words that have ര in them. But the claim is that there is no pure Tamil word starting with ര. You always have a vowel (usually ഇ) preceding it. e.g. ഇരവു, ഇരണ്ടു, അരചന്‍്.

I didn't read anywhere that there is no pure Tamil word starting with ല, may be I didn't read enough. But the hypothesis seems very plausible when I think of the words starting with ല. E.g. ലക്ഷ്മി, ലവണം, ലഗാന്‍്, etc. ലക്കു് sounds like a possible candidate, but it is possible that it is a തത്ഭവം of ലക്ഷ്യം (ലക്ഷ്യം -> ലക്കം -> ലക്കു്)

I didn't read anywhere that there is no pure Tamil word starting with വ. Of course, there are tons of words that start with വ.

So why is വ different?

If we consider the next four alphabets (ശ, ഷ, സ, ഹ) we see that there are no pure Tamil words starting with these letters as well. It is conceivable that these sounds came directly from Sanskrit. They don't appear in common pure Tamil words.

But യ, ര, ല, വ appear in pure Tamil words quite frequently. So why only വ is used to begin words and the others are not?