[Hawthorn]

Say that again? The Tocharians didn't indulge in the early palatization of their velars?

Truly shocking beyond belief!

[Verginius Rufus]

A simpler explanation is that the Indo-European languages can be grouped into two categories, the centum languages and the satem languages, after the word for "100" in Latin and in Avestan. There is a consistent pattern where the K sound in the one group corresponds to the S sound in the other. In the Germanic languages the K became an H sound--so Latin centum, canis and cor correspond to English "hundred," "hound," and "heart."

The Indo-Iranian languages (including Scythian) belong to the satem group (along with the Slavic languages--Russian sto for 100), but the Tocharian languages are centum languages like most of the European languages--they are not closely related to the Indo-European languages nearest them geographically, such as Sanskrit, Scythian, or Persian.