I've found a 737 maintenance planning data document produced by Boeing, which gives a suggested schedule on page 6.
I've also found a British Airways Fact Book document, which on the last page gives a schedule.
So who decides how often an aircraft and its individual components should be inspected? Is it the manufacturer, the airline, or somebody else? Is there a set standard or does this differ between manufacturers/airlines/countries?
The manufacturer lists all maintenance that should be done, and when. This is the first document you found, from Boeing. Some of this maintenance may be required, other things might be recommended.
The operator can use that plan, while following maintenance laws (e.g. the required annual inspection). Or, they can submit a new rolling maintenance plan to their National Aviation Authority (e.g. FAA) for approval, which is usually done to prevent large downtime events for the aircraft. (This "rolling inspection" is done so that all of the necessary things are inspected at the proper intervals, but not all at the same time.)
There's a bit more, too: the Aviation Authorities can create Airworthiness Directives that can add additional required maintenance that must be done within certain limits (usually hourly, but can be situation dependent) for the aircraft to be airworthy.
Just came across this post I realize it's a bit dated but the information given here is a little incomplete.
The OEM sit the initial intervals for most maintenance items. If you are a 121 certified Air Carrier with an approved Reliability program, Operation Specification D074, then with the proper analysis you can adjust the intervals for those tasks not governed by regulation, such as Air Worthiness Limitation items (AWL's).
