I've never understood how Alexa stats are considered relevant. No-one I know - from the savviest sysadmin who only browses in lynx to the most malware-infested bloated-PC user - has ever used Alexa toolbar. I once installed it a long time ago on some random machine just to look at it and uninstalled it again. How is their traffic 'representative'?
You can make this claim for any headline referencing web traffic figures, and while it weakens the headline, losing a quarter traffic over 2 weeks in any market is still noteworthy at least to me.
FWIW, addons.mozilla claims 56,000 users for the Alexa Firefox toolbar alone.
Does Gallup poll every US citizen? These stats are sufficiently random to mirror trends, especially when there's not many other ways of getting this information.
Those statistics are enough to sample the entire population only if it is a fair sampling, but I think the point is that Alexa toolbar users are not a fair sampling of Internet users in general, and hence the claiming that 27% figure applies to all 'net users is inaccurate and misleading.
It is closer to fair sampling than you think, since the average internet user is more likely to install toolbars unlike the technogeek niches that we hang out in. Also, it's more useful for relative changes like drops and increases rather than absolute percentages.
Also, it's one of the only few samplings we have, unfortunately.
I think you missed my reference to your specific point.
"No-one I know - from the savviest sysadmin who only browses in lynx to the most malware-infested bloated-PC user - has ever used Alexa toolbar."
I'm one of "those guys" who everyone comes to in order to get their shitty computer fixed for free. I've seen a lot of "normal users". I do not think that Alexa users are a representative sample based on what I've seen.
