I think the reason for this is that it might be a little strenuous on the client's JS processor to do that (sure not for up-to-speed browsers on decent PCs - bu

I think the reason for this is that it might be a little strenuous on the client's JS processor to do that (sure not for up-to-speed browsers on decent PCs - but usrers on slower systems may encounter some sluggishness). Also there's some server issues to be taken into account. I wouldn't be surprised however if later on they decide to deploy advertisements - making the user stay on the page for longer is a good tactic to try and get them to click on an advert.