Really, what's the difference?
 

Between a well built suspension hybrid like a Specialized Crosstrail, or Trek DS and a hardtail mtb 29er?
OK, so the tires are a bit wider but that's easily fixed. Frame strength? Wheels?
I suspect that an experienced rider can go virtually anywhere on a hybrid. that a 29er can.
I know I'm not sophisticated about such things but it seems to me that the only things different are visors on helmets and baggy shorts.

bored at work?

Sort of like a corolla and a jeep. Both have wheels, both can go on dirt roads. Can go on the same trails? Yup. Going to fit 2.3" tires on a hybrid? Not likely. 50 mm travel vs 4-5". Steering and geometry, way different too. Rim width, gearing choices, frame strength and weight all different. But the 29er hardtail can do anything the hybrid can, just put some slicks on, start there.

The better question is what are the differences between a rigid fork mountain bike and corresponding hardtail with suspension fork. If you ride slowly and carefully enough, and providing that you can get the same dimension tires (a huge "if"), and you're strong and technically skilled, the differences aren't that much.

If you ride aggressively, the differences between a quality front suspension and a rigid fork become quite pronounced for ground tracking, stability and bite when the $#it hits the fan.

As for road hybrids and suspension fork hybrids, they're different entirely. They don't compare well to what a good MTB can do. The differences are like between Honda Pilot and a HUMVEE. If you want to drive on an improved gravel road to your favorite winery, then they're equivalent. The Honda will be quieter and more comfortable. If you want to go over stumps, ford streams and rockbeds, and plow through saplings, all at speed, then don't take your Honda.

Nah, retired. LOL

An urban 29er is like an SUV. Take it anywhere.

Mine comes with a rigid fork and I find I don't miss a hardtail bike.

With a skilled rider pushing these bikes near their limit on varied terrain, the differences become much more apparent. For dudes like me who simply ride around the neighborhood for some exercise any of them will work just fine and any differences will be much more subtle.

Geometry and fork travel, and quality of the fork are some differences. The 2016 Crosstrail Pro Disc has a Suntour coil-spring for with only 50mm travel, whereas the 2016 Crave Expert at the same price has a Reba SL air fork with 100mm travel. The longer travel is more suited to offroad riding, plus the 100mm is a much more common fork travel distance making it easier to find replacements and upgrades.

ETT is shorter on the Crosstrail at 585mm versus 604mm on the Crave, for the two medium frames. That's enough of a difference to matter. I once owned a first-year Crosstrail. The shorter top tube in comparison to my mountain frames was mildly annoying and forced me to run a somewhat longer stem than I would have preferred to run at the time.

Tire width. I haven't examined a Crosstrail closely in a while, but I'm pretty sure the rear triangle of the frame constrains tire width. That appears to be the case from looking at the photos, and my guess is that you can fit wider tires to the Crave.

But I'll agree w/the OP that a bike like the Crosstrail can go pretty much anywhere that a similarly-designed mountain-bike can go. Sure there are differences, but a halfway decent rider would compensate for them and keep on going.

Whats your objective?

I'm thinking that you are probably right thinking that a hybrid bike can be ridden almost anywhere. If that's your objective, go for it.

If you are thinking that a hybrid can be almost as good as a real mountain bike for real mountain biking, you might want to think again. It's everything. All the little details add up to make a purpose designed bike better for it's specific purpose.