Does 4e change the viability calculus for a tank-centered campaign?

[Heffe]

Definitely an interesting thread. Regarding ammo and parts - I've spent a completely unreasonable amount of time studying the 4e OrBat info. Out of curiosity, I went back into the 2e books to find OrBat info for comparison, and it seems like there's a few items of note:

1. Units in 4e tend to be a little more consistent in terms of their manpower still available. Where a division in the older editions might have anywhere from a few hundred men to ~5000, in 4e they generally have somewhere between 1-3k personnel. 4e brigades typically have between 400-1200 manpower.
2. The older editions seem to mention tanks exclusively for vehicles. 4e, by contrast, simply mentions "Combat Vehicles". Looking at the US 1st Cav in particular, in the older versions it had a combined 48 tanks. In 4e, it's listed with 47 combat vehicles. Other units, when there's a comparison available, can vary drastically.

In short, from a ammo supply/spare parts perspective, I'd expect 4e to be somewhat similar to the outlook in the older editions. Though as you've noted, 4e's spare parts rules tend to be a little more forgiving than prior editions.