Originally posted by JHD Well, let's keep things in perspective. The OP of that thread may or may not have an issue with his 100WR as it's not clear from reading the thread whether or not he actually has an issue or not. That said, let's assume for the moment that there is an issue with his 100WR that requires warranty service. If this was a QC/manufacturing defect than it would be covered even under Pentax's (short) warranty coverage (1 year in the US, 2 years in Canada).
So the question becomes what are the chances of an issue coming up on a 100WR lens during year 3-10 (in Canada) or year 2-6 (in the US). The actual numbers aren't known, but as I said in a previous post, I believe the chances are fairly small with lenses like the Tamron 90 and 100WR. Let's say 1 in 100. Let's also assume that a out-of-warranty repair would average $200. So the "value" of the extra warranty period is worth somewhere around $2 in terms of expected value, statistically speaking.
Contrast that to an SDM vs HSM warranty situation, which you are quite fond of pointing out. In this case, let's say the chances of an SDM failure during the difference in warranty periods is 10 out of 100. Using the same repair cost, that would place the value of the value of the extended warranty in this case is $20. Now, I'm sure you'd contend that the probabilty of an SDM failure during the extended 5+ years is substantially greater than 10%. So let's go with a number like 50% and a repair cost of closer $250. Now the extended warranty period is worth closer to $125. In this case it might become a factor when comparing two lenses (unlike the above case comparing two screw-driven lenses where I believe the value of the warranty period beyond the first year is somewhat insignificant).
edit: So to the OP, if you do decide to buy the 100WR, I would personally buy the gray market copy over the more expensive copy at a savings of $190, so long as you still have a return window should the lens prove to be defective upon delivery. This is the same reason/logic I use to justify only buying used lenses. The cost savings is substantially more than I would ever spend on repairs for lenses than seldom need service. Even when it comes to lenses which have a higher probability of failing (like SDM lenses), the cost savings is almost always higher than what you take on in terms of risk.