Notepad, Address Book and Calendar are already tightly integrated into My Yahoo, which is what the current Yahoo homepage was originally derived from. Delicious was always an outsider in comparison.
Because of that tight integration, I guess those features are tended to be used by certain coveted audiences of the My Yahoo product - like people monitoring their stock portfolios using My Yahoo. So there's enough of an ad-happy audience using those features to make componentising these features - perhaps as YAP modules - throughout the range of Yahoo sites.
Though, as I understood it, Yahoo notepad hasn't had any tender loving care for years (it was something I was interested in redeveloping during my time at Yahoo). It's not much more than a persistent textarea (unlike the defunct Google notebook that had far richer structure)