Many folks put a lot of miles on Enduro's, when not raced they do not need as much servicing, just think of road bikes used exclusively on tracks, they go from needing a service every few thousand miles, to every handful of track days - down to hundreds of miles from thousands, its the opposite way around when bimbling about on an Enduro bike.
The bigger the Enduro the harder they are to thrash and less mantenance needed, a lot of folk in the US use 500's as "Dual Sport" bikes and report pistong lasting 20,000 miles, even 350's reportedly manage 500+ hours on a piston - 10,000+ miles, and I just gave my husky 350 a top end overhaul at @150 hours and the piston was in excellent conditon and the bore looked like new (I was always a bit concerned the hours on it when I bought it may not of been genuine - but now think they probably were accurate or fairly close.
You also need to consider if taking a road based trail bike like a DR and then riding it almost exclusively off road you will need to do a lot more maintenance than the manual suggests if you want it to last, so the differnce is a lot less than some people imagine, although obviously a CRF250L will have a longer engine life, it is also bloody heavy (40kg more than an Enduro) underpowered and the suspension needs upgrading, an Enduro will be pretty much fully sorted out of the crate.
Also the "hour meters" only clock up when bike is moving, I often gone for a "long day out" to find I have clocked just 4 hours or so, and it's easy to stretch service intervals to 20 hours for trail riding, giving you 4-5 days riding between a simple (and cheap - they don't hold much) oil change, the 10 hours in the manual assumes you may have spent 10 hours in sloppy welsh bogs at WOT bouncing it off the rev limiter in 2nd the whole time, pootling down a lane at about 1/3rd of that RPM on a whiff of throttle puts a lot less stress on them.
Another consideration is they are deisgned to be maintained regularly, parts are relatively cheap, a full set of genune OE bodywork for my Husky listed at just over £200 inc vat about 5 years ago - side panels, rad shrouds, headlight surround, fork protectors, tail piece the lot - a lot of road bikes will cost that for a single panel.
It just so happens my 350 is for sale, just had a good overhaul and should need nothing for quite some time;
