Not to be offensive, but do we really think William is so maudlin that holding his wedding at Westminster Abbey would be awful for him? Two funerals were held there for beloved family members, and they're hardly going to be the last - assuredly his grandmother & grandfather's funeral services will be held there also, as will his father's and possibly several other family members as time marches through his life.
I don't doubt that William probably would want to avoid St. Paul's, not just due to how his parents' marriage turned out, but also because of the sheer size of the venue. But he's not this tragic figure, nor does he strike me as the type to rule out a venue like Westminster Abbey simply because that's where his mother and great-grandmother's funerals were held. How many of us would choose to not get married in the "family church" simply because memorial services for beloved family members had been held at the same venue? Granted, it's hard to know if William considers Westminster Abbey, or any church in particular, to be the "family church", especially as he's likely attended services at many churches on a fairly regular basis over the years (Christmases at Sandringham, probably a lot at St. George's Chapel, etc). But, I just can't envision him even making an argument against Westminster Abbey simply on the basis of it being the location of the major family funerals.
I honestly can't imagine him getting married in Windsor at St. George's. My money's on Westminster Abbey.