Now, first up, I'm referring to the content of the page - NOT the layout of the adverts.
I've just been having a royal rant in another thread about SmartPricing and I struck upon an idea. If your smart pricing is based on your quality of conversions at the advertiser end relative to their median conversion rate, then it would make quite a bit of sense that long-term pages return better EPC's. . . .why?
Why... because it means that the adverts for that particular advertiser have had a chance to be exposed and probably clicked on several times (and hopefully resulted in a conversion), thus giving your page a potentially better conversion rate and hence better smart-pricing.
I personally have watched my EPC on various pages oscillate high and low with a dampening trend... trending to perhaps what is my "true" conversion rate induced smart-price adjusted EPC.
When you change the content on your pages it quite frequently causes the adverts to go random again for several days even weeks, meaning that a given advertiser cannot accurately establish your conversion rate again.
... anyhow, that's a theory - it would appear to fit my own personal data. Anyone else?