How many significant digits do you consider acceptable? Even in an ideal APS environment, link failure detection and protection switching does take finite time. You might get 99.999% uptime, but probably not 99.9999999%.
The thing that always got me was that there never seems to be a mention of the sampling period for the stat.
Methinks that you've been subjected to Marketing. ;-)
Well ... I'll give you 99.9999999% on any system you like - with a sampling period of say every billion years. I think that allows me to stay down for the first 100 years, long enough to extend beyong the life of any stressed sysadmin :) More seriously - SLA's that specify a sampling period then also give an indication what is considered too long an outage. If you get just under the .1% downtime allowed per year all in one go you may well be pretty pissed at being told the 8 hour outage was within the SLA. Manar