While its not clear here whether technology maturity was a feature of the competitive process for the Tanker or not - it would be quite reasonable for it to be a factor.
Unproven technology (or that with a low Technology Readiness Level or TRL, a NASA metric for measuring such things) is always associated with cost, performance and timescale risk - considering this should always feature in any procurement decision making.
You would normally only consider high technology risk projects over more established technologies if the performance benefits were essential or worth it (F-22 vs F15) or they offer cheaper long term benefits (e.g. investing in risky hi-tech production automation worth it due to massive cost savings downstream). It doesn't look like the Boeing 767 tanker falls into either category however, so the "paper aircraft" vs "real aircraft" should actually be quite a big issue, politics aside.