Eliveleth,
This is a rather common way of explaining the genealogical difference away, but imo it runs against the texts; both Matthew and Luke present their genealogy as that of Joseph, not Mary (Matthew 1:16; Luke 3:23).
To the thread topic, I don't think any of the canonical Gospels implies Davidic descent for Mary (nor do they rule it out).
Otoh (now that I can see nomoreguilt's question on the other thread) it is not entirely impossible that an early stage of the Matthean genealogy did not consider the idea of a virgin birth, which would solve the issue as far as Jesus is concerned. For at least a Syriac manuscript of v. 16 has: "Joseph, to whom was betrothed Mary the virgin, begot Jesus who is called the Christ."