Hi Rob

The reason your Cessna 150 doesn't have or require logs like the homebuilts
is that they (The type certificate holder, Cessna) has a production system
and QC system that satisfied the FAA that Cessna could build aircraft
identical (or nearly so within limits defined by Cessna and agreed to by the
FAA) to the first one certificated of that type.  All production stages have
to be performed by a Cessna emplyee and signed off by an inspector and any
stage may be inspected by the FAA or a representative.  Your plane will have
a log on record at Cessna that showed when each part was built and signed
off, what engine it had in it, weight and balance, etc.

Dan Newland