So how does Compete.com know that "many major sites have declined in their traffic"? Do all the major site operators disclose their traffic figures to it? Or, is it just an estimate based on who-knows-what method?
My point is that you shouln't necessarily believe any figures unless the person stating them can demonstrate how they were obtained.
But even if your supposition is correct, it's got nothing to do with how your site or my site is doing. Nor is it connected with SEO or Google algorithm changes, since any change that pushes a site down would push another site up.
I doubt that the economy is a factor either. Was the economy (of the entire world) in overall better shape ten months ago than it was today?
Personally, I woulnd't worry about any of this.