Tabular data on commons supports marking the source of the data, but only as a single source for the entire table, which does not match how data tends to be sourced in real life - often every row, column or cell of a table has different references. (Examples: per-row, per-column, per-cell.) Although much rarer, other types of annotations (plain textual notes, not sourcing, e.g. comments on methodology) are also sometimes used, and also can be on row, column or cell.
If tabular data is ever to serve as the primary way of storing data (as opposed to an intermediary for data taken from external sources or parsed from a wiki table), it needs to be able to support cell-level references and notes. Ideally column/row level too, although one could hack around that by providing an extra column or row where the cells contain nothing but sources.