Without knowing exactly why, my feeling is iframes are broken. If not.. why arent iframes used in say yahoo and google customisable home page mashups? Differe

Without knowing exactly why, my feeling is iframes are broken. If not.. why arent iframes used in say yahoo and google customisable home page mashups? Differences : granularity - share one div, not whole page scope - how should javascript interact between the inclusion and the whole page? [ Im not sure.. this wasn't on the radar when iframes were designed I guess ]