On the HTML markup, there are many valid reasons you may want to use non-TABLE based tables:
- it allows better rendering control for infinite scrolling (DOM reuse, re-positioning, detached view for sticky header and column)
- it allows you to have real (CSS style-able) row groups, or if your structure is hierarchical, it allows you a better control to create a treetable (reduced rendering time if you expand a node and insert a bunch of rows in the middle).
- it allows you to have multiple grid systems inside the table (e.g. a detail row may use up the entire row, and it may have its own table inside, which you'd like to synchronize across multiple detail rows). I guess this later benefit is just redressing the fact that you do need to implement an independent grid system anyway :)