don't forget that the desmo 'service' can ammount to not much more than a clearance check with nothing being done if they're all in tolerance.
in the case of a 749r whos heads are a work of art they rarely if ever need checking unless they're being used on track.
Even belts, if you're going to lay the bike up for a very long time, just slacken the tension off, and retighten when you recommission the bike, failing that once every couple of weeks get your crank turning tool in there and spin it around for a couple of minutes - which gets the oil pump doing its job as well, and should be something you do when recommissioning an engine anyway as it means you start to pump oil without cranking the thing over - especially on an injected bike which starts fuel priming and spraying the minute the ignition is turned on.
Also as
@BobTheBounder and
@WAYNE have touched on, there's manufacturer due dilligence and safety factor to consider. If gates / ducati etc. are telling you that 2 years is long enough for those belts, then you can be sure the safety factor is 25-50% that again. No manufacturer is going to put their cock on the block and engineer something without some major slack in it becuase you always design for the lowest common stupid denominator i.e. the customer, unless you're a race team, where you're literally trying to design something that will last no more than the full race distance plus the time it takes to roll back into the pit garage - at which point it can shit itself royally as it's job is done.
A belt four years just tuned by hand every couple of weeks (total of probably what, 20 revolutions) is different to a belt that's been run under load and in anger for two years. Turnt he thing by hand and you still probably won't subject it to the loads it sees in one minute of actually idle running.
my last one until 2 years ago was nearly 20 years old 
