>PIE had a vowel (how come this "Ablaut vowel" doesn't
> have a > name?) which was realised as e/o/nothing.
>
> How about calling it Vedic a.
Because it was not Vedic a. It is important for our understanding of Vedic
(and Sanskrit) that we acknowledge the presence of an original /e/ and /o/
and /a/ as separate vowels in whatever we call the source language of Vedic.
It is important for our understanding that we recognise the triple origin of
Vedic a.
This Vedic a also has as its source some PIE /e/ and /o/ and /a/ vowels
which are not in ablaut, so to call the ablauting vowel "Vedic a" would be
wrong for this reason as well.
Peter