I would assume comments are tied to gmail accounts or some other unique identifier. We simply also need to be able to rate the comments themselves, which in turn would rate the commentators. Pretty soon, you can filter to only see comments from commentators with non-negative ratings. They do that for some blog comments.
They really do need to expand the amount of information allowed for product information, like sub-sections for a full description, screenshots, version history, support info, etc. If you check out the android.com website, they offer much better info on market place apps. It seems like google only allows for a small amount of product description text since I see some programmers replace the product description text with support info. It's kind of frustration trying to figure out what a product does when the description says, "This new version fixes xxxx and yyy. Give it a try!" Okay... what does it do??!!!