The Osprey is a complicated hybrid aircraft. How many other aircraft have transmissions with drive shafts running between the engines so both props can be driven in the event of an engine failure? How many other aircraft have pivoting engines and combine the controls of a helicopter with a fixed wing airplane? Think about that for a moment: visualize the engine/rotor movements necessary for pitch, roll, and yaw control in hovering flight. It isn't simple.

The Osprey has had more than its share of quality control and maintenance issues. It has been in flight test for several years and they're still working the bugs out of it. The two fatal crashes last year didn't help. The first crash killed 19 Marines and appears to have been pilot error. The other crash killed 3 of the most experienced Osprey pilots/crew anywhere. That highlights another issue - training people to fly the vehicle. They'll need helicopter and fixed wing experience and time to get familiar with the hybrid between the two. Some things simply can't be rushed.

I fully agree with your point about previous planes losing prototypes only to go on to very productive careers. Here are but a few examples:

B-17 - prototype was lost when they tried to take off with the elevators locked)

B-29 - prototype caught fire in flight and crashed)

B-26 Marauder - they lost so many of the early ones that they squadron slogan was "One a day in Tampa Bay"

XP-38 - prototype lost on transcontinental speed dash. Several of the other early P-38s were lost due to compressability.

P-47 - some of the early ones had a problem with their tails and crashed.

P-51 - prototype crashed

P-80 - several of the early jet fighters crashed, including one that killed America's all time leading ace, Dick Bong.

So many of the late 1940s through 1960 planes crashed during test flights that Edwards AFB has no shortage of street and building names. Each was named for a pilot killed on a test flight.

F-14 - something like 12 of the first 14 of these planes crashed. The prototype crashed on its second flight due to hydraulic failure.

YF-16 - prototype's landing gear malfunctioned, pilot bellied it in but the plane never flew again.

YF-22 - prototype was lost due to malfunctioning flight control software

B-1A - one of the prototype planes crashed in the 1980s during an aft-CG test.