There are deeper reasons for answering in comments, than just laziness, I believe. I think this trend reflects the limitations of the SE model. What really happens is that often, one does not have the time for a proper answer, also because properly answering often gets one involved into subsequent discussions, corrections and what not - so it is a lot of extra responsibility which we are not always ready to accept, and not for every question.
Comments also often can give hints to less experienced users, who might still use those to produce good answers. So, in a way, I view answering in comments as a tool to help get more people involved in answering, and take some load off the main core of experts on the site.
This is not to say that I fully agree with the strategy to answer in comments. I just think that it has its uses, when used with care. The uses I appreciate range from posting half-baked ideas / answers, to answering very simple RTFM - style questions, to giving experienced folks with little time on the site a light-weight way to help.
I also fully agree that eventually, comments should be transformed to answers. I think that whoever posts the comment which (partly) answers the question, should make an implied promise to revisit the question at some later point, and convert the comment to a full-fledged answer if no answer has been posted. The community can also be helpful to remind such posters about such cases - like e.g. you did for a couple of my comments to questions which happened to remain unanswered.