With an expected ROI of something like 20-30 days, I'd be more than happy to mine profitably for four months only to trade up to a new gen device. That would still be a profit overall, even after paying for the new device, plus you still have the old one hashing all you like for another 8 months viably at least.
If you don't trade up as tech advances, you eventually get left behind anyway and will be forced to stop mining. Some will be happy with that, others, not so.
I think what is confusing people on the ROI, is that we are suddenly dealing with start-ups that have no money in the ASIC world.
We have been use to doing a rough calculation, going down the shop and buying the latest GPU, and starting mining. But now it's all changed, because the ASIC companies have no money, they have to go into this pre-order caper and accumulate funds to pay for the fabrication. That introduce the many month delays (in the case of BFL over a year) in the ROI calculations. This is a concept people can't get their heads around. Hopefully the ASIC companies will eventually work out better ways of funding their next generation products, like the GPU companies do, and announce product when it's ready to ship.