One reason that the Stas delegates show low uptime is that the uptime is figured from the first block that the delegate forged. In the case of stas, that is around 110,000. we are now in 270,000 range. Stas was offline for a few days due to a billing problem with Vultr. Since he missed forging some 50,000 blocks, he dropped to about 14%. It takes about 100,000 blocks for him to advance 15%. He is forging around 100% now.
This is t change in version 021. The uptime will be figured with the last X blocks. Value of X is undecided, and depends on testing results.
This will be a valuable change and similar to what I proposed earlier about "current consecutive blocks missed" being a figure of merit that needed to be shown. I still think this would be the best thing to show for making voting evaluations, not an "uptime" number that blurs this info by "averaging" it over "t".