I understand where your all coming from but while specifics about the PoO haven't really been discused in the show if the show's navagational co-ordinance are based on any kind of science fact then you would have to account for planetary drift with both the destination and PoO otherwise the science in the show would be a complete contradictory joke.
Also the fact that you can dial manually with out computors or DHD means the gate has to store the co-ordinance related to each symbol. Also in the ep Red sky the gate knew that they would pass through the sun even tho the SGC computors didn't. The DHD seems to be needed to update and program the gate but the gate has to have a redundent memory for situations where the DHD is lost or out of power.
The main problem with the show is that there are too many continuity errors regarding the gate so we dont know whether we are coming or going.