Conversations being split can be a feature; I know vaguely what to assume when writing for the audience here, but not at random other sites to which my comment could be syndicated without my knowledge.
And if that other audience responds there, I may not know, and if that other audience arrives here, the quality differential you've observed may evaporate.
A tech blog did this with HN comments at one point and I registered my strong objections in that thread:
I wouldn't object about my own comments, because I'd opt out. I'd still have doubts as to whether it was a good option for the community, but that's really up to PG and the YC crew.
BTW, signing your comments is discouraged as redundant, since your username already appears and you can put more info on your user page. See the site guidelines: http://ycombinator.com/newsguidelines.html
And if that other audience responds there, I may not know, and if that other audience arrives here, the quality differential you've observed may evaporate.
A tech blog did this with HN comments at one point and I registered my strong objections in that thread:
http://news.ycombinator.com/item?id=639874