These are to do with the physical connector rather than the protocol being used.
(We don't call analog connections "XLR" "RCA" "3mm-jack")
I'd suggest a more descriptive tag would be Matrix:Tag-SPDIFio
For instance many AudioScience cards support software selectable AESEBU or SPDIF for digital I/O. The connectors are XLR. They don't have RCA connectors.