dbr has explained that technically YTM doesn't assume anything about what's done with the coupons--it's just the discount rate that equalizes price and future cash flows, and the math doesn't require assumptions about what's done with the cash flows.

The way I put it is that for the realized return to equal the initial YTM, all coupons must be reinvested at the original YTM.

So I think it's OK to think about it the way you state it, even though it isn't technically correct. My investing textbooks frame it this way, even though it's not technically correct.

I guess you could say that. Again, the realized return is unlikely to equal the original yield, because the coupon reinvestment rates are unknown.- Therefore, if I'm buying these on the assumption that Treasury yields are going to go down, it will be problematic to reinvest the coupon at the same rate and the same level of safety, so that I can regard the yield as meaningful?

The lower the coupon, the closer your realized return will be to the original yield. A zero coupon TIPS would make them close to equal, and a 0.125% coupon TIPS is the next best thing.- Therefore, I would be better off--no, I would have a SIMPLER problem--if I seek minimum coupon associated with corresponding price discount?

As dbr said, internal rate of return is akin to YTM, since both are discount rates in a cash flow analysis. Coupon affects the duration and the risk that realized return won't equal original YTM. So I look first at yield, and then at coupon.- So that I'll get my money later, but that's built into the yield calculation and in theory, I end up the same in the end? I realize that it depends on precisely what I buy and the price that minute; I mean, the tendency is that low coupon may get a discount, high coupon may get a premium, and the yield calculation's precise job is to tell me whether I end up even?

Note that in a non-rolling ladder coupon doesn't matter, since we're spending the cash flows, or otherwise removing them from the ladder. Larger coupons in later years result in few TIPS being required in the earlier years, and vice versa.

Remember that if there is deflation, things will cost less, so your purchasing power still is preserved with TIPS. With lower index ratios, there's a higher probability of a return bonus if we have extended deflation, due to the face value lower limit of the adjusted value at maturity.Oh, and of course there's the adjusted principal and how I feel about that, the odds of deflation, and how it will affect me in the case of deflation. But the yield has nothing to say about that, I believe.

Also note that it has been many, many years since we've had any period of extended deflation.

Considering the above points, many of use, including me, pay little to no attention to index ratios (aka inflation factors).