LH (usually) only upgrades people when the lower class is overbooked. This does (and must) happen from time to time and depends on the route and the season.

From my 3-year-LH experience I can say that those op-ups are not standard and if they occur the number of op-ups is low.

For sure, they should not operate a 747-version with 80C (highest c-pax number as far as i know on LH aircrafts) pax on routes with high Y-demand in summer, however, this may have operational reasons...