the linkage between that and the use of "wr" as being a causal relationship.

Well, failing lslslsls coming back and explaining I can only say that I didn't read that assumption into the words. The words in question start with wr because they are a subset of the wer- rooted words that do that. There were other groups of wer- rooted words that don't have that and some words that start with wr that don't come from wer-. Wright, for example, comes from werg-, to do. But other than that all the words in the AHD4 that begin with wr and are traced back to PIE trace back to wer-.