The FAA has said in the MacMillan letter that manufcaturers can not establish a mandatory schedule for maintenance. They can reference FARs and ADs to make it legal, and they can put their requirements in the FAA approaved Limitation or other FAA approved part of the POH and make it stick. But the Flight Design 100 hour inspection is not enforceable.
This is not to say it may not be a good idea. That is not the issue. Anyone who wants to exceed the legal inspection schedule can do it (albeit at the risk of maintenance induced failure).
The letter is long and convoluted, but the bottom line is pretty clear. As you may guess, the way manufacturers are getting around this is to make a modification to their product, get a new Type Certificate Data Sheet (TCDS) and incorporate their will in it. But, I'm not sure how that plays in the Experimental market.
http://www.faa.gov/about/office_org/hea ... Millan.pdf
Good luck reading it through.
Manufacturer Can't Set Maintenance Schedules
Moderator: drseti