Compensatory lengthening

I don't understand the compensatory lengthening Latin pe:s,
Greek pous. I seems to me they are compensated for something
they didn't quite lose. There is not much phonological sense
in a rule that removes part of the consonants in auslaut. All
or nothing I say. It must have been nominative pe:, in composites
-i-po:, and the nominative -s analogically restored later.

Similarly in verbs with the secondary endings.
Let's take *bhudh- "wake up, be present"

*bhudh-om
*bhudh-s
*bhudh-t
...
*bhudh-ont

becomes

*bhudh-om
*bhu:
*bhu:
...
*bhudh-ont

from which we may extract two roots *bhudh- and *bhu:-
(and we don't have to write *bhuH- any more)


Torsten