He said they are using no method, no weighting what so ever.
Yes — after pointing out that they ask the affiliation question second. That would still enable them to use the second method I mentioned (weighting during analysis). Gallup chose not to do this. If you have reason to believe that Republicans are less inclined than Democrats to talk to pollsters, then Gallup has made a serious error.
If the proportion of registered Republicans, Democrats and Independents does not closely match the known proportion of each in the population; then you have a selection bias problem. Plain and simple. And, BTW, this has nothing to do with the way each respondent actually intends to vote. It has everything to do with matching the sample to the population.