In 6.1 and 6.2 the portlets were able to search in comments. For example, Blogs portlet would allow to search in any comment added to a Blog Entry. The same happens for most of the portlets.
In Liferay 7 we are removing the search in the particular portlets in favor of the general search because we don't want to have in the same page multiple searches. However, the General Search doesn't search in comments.
We should include this feature to allow users search in comments.