I think that is the crux of the conversation - it all depends on who you are and what bike you're on... 100°F would be murder if you were all togged up in a Klim 'adventure' suit on a 1200GS loaded with hard-luggage and spare tyres, constantly dropping your behemoth on a sandy two-track in the middle of the desert.

Conversely if you are on a lightweight dual-sport, with minimalist luggage, fit and experienced, nothing in even Kevin's 'hard' routes ought to be overly taxing (although like you say, 'dirt-bike' routes such as the Rainbow Trail can still be a bit much, and have caught out plenty of 'cross-country' riders who are already two or three weeks into their trip, with the associated fatigue) - but I suspect the reason Sam has chosen to re-route along 'easier' trails is because he knows the typical customer who wants to purchase a pre-defined route is likely to be less experienced and/or looking for something other than a 'hard-core' challenge as they cross the country?

Certainly those few riders I've met on and around the TAT route tend to be middle-aged and on overloaded bikes like KLRs - not riding 500EXCs with just a tail-pack... and I suspect Sam knows that too.

As for the 'quitting in Moab' thing (just a have a read through some of the TAT reports on ADVrider for example) - again I suspect it because those riders started to suffer the compound effect of riding day-in-and-day-out for at least two weeks by the time they get to Colorado, only to be faced with significantly more challenging terrain and altitude - increasing their fatigue and the chance of making a clumsy mistake. I suspect a lot of people also under-estimate how long it actually takes to ride the complete TAT route (at least as closely as possible, and with the odd stop to sight-see en route) and realise they aren't going to make it all the way to the west coast in the time they allotted.

Ultimately I think you and I are both on the same page here (other than how much the respective predefined route providers ought to charge for their work) - at the end of the day, a pre-defined TAT is just one person's suggested route across (or around) the country... To really make the experience unique, and fundamentally suited to your own requirements, it makes sense to gather as much information as you can (BDR routes etc.) together, and plot your own route to take in those elements most important to you, and which is achievable in the time frame you have allowed.

And add a extra week to that ;o)

Jx