tire balancing and TPMS sensors

I just bought 2 tires online (Continental ProContact EcoPlus, tires-easy.com, $82.70 each incl shipping) and had them installed and balanced at my local Walmart Automotive shop ($12.50 each incl lifetime rotate & balance). The manager told me afterwards that it took an excessive amount of weight for both tires to be balanced (around 4 oz, I don't know if that's excessive or not). He suggested that the problem might be with the tires (both of them?!). I wondered if the 'excessive' weight might be necessary to compensate for the TPMS sensors instead of ordinary rubber valve stems. Has anyone else run into this 'problem'?