Amtrak's practices aren't out of line with what you see on VIA (though even there, IIRC, you've still got a "full flex" sleeper fare), where you basically have "Escape" (Saver), the intermediate fare (Value), and the full flex fare (Flexible). One thing this does trigger is a "push" towards Business Class, which is very much at odds with the pricing structure I saw in the UK.
Of course, this also in practice stands in opposition to the practices on most airlines, where usually flexible/refundable fares are also variable (roughly in line with the non-refundable fares). For example, on JetBlue, the "refundable" fare is (IIRC) a pretty standardized $200 surcharge on whatever the prevailing "full" fare is. If nothing else, doing this helps to time-differentiate some of the full-flex crowd (e.g. you don't want them to all become time-agnostic if you can "nudge" some of them to a lower-demand train, since [for example] you'd probably just assume bump some of them away from the 5PM Acela (which will sell out or close to it) and to the 7PM Acela (which might not be anywhere near to selling out). I mean, it's fine to sell out that peak train, but all else being equal you'd probably rather fill seats on those other trains and still enable walk-up/last-minute sales if possible...especially since this is going to "push" some folks to full-flex tickets.
Edit: And of course, the fact that they're doing this without a flexible sleeper ticket did make me wonder "What, they're not able to rip enough of us for travel insurance?" I mean, c'mon...peg the flexi-sleeper one bucket up from the non-flex sleeper and I can tell you that there are some of us who will shell out for it...and I can speak to at least one other member of this board for whom this is basically a deal-breaker on LD trips.
Edited by Anderson, 24 March 2018 - 11:28 PM.