Until a year or two ago there was a stalemate as far as "rich web" development technologies goes. Neither flash, Silverlight or HTML5 was the clear winner. I remember people being incredulous that the iPad didn't support Flash, saying that while it might be ok for the iPhone to not support it, nobody would take the iPad seriously if it didn't support Flash. In a way, I think it might be the combined weight of the iPh…
Two years ago, flash was the only game in town; Good HTML5 implementations were no where to be found, and Silverlight adoption was a joke. It's not like you could HTML5 an equivalent to flash on an iPhone OS 3.
I agree that things started changing rapidly two years ago, with the introduction of iOS 4. But there was never a stalemate -- Flash was king; then there was chaos; and now HTML5 is winning (for the time being, though not for long, Flash is still among the royalty). Silverlight had always been a wannabe.