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…
For the last three years, I'd find anyway to build a RIA in anything but JS/HTML. I'd use GWT/Cappuccino/Silverlight/Flex, etc. After Microsoft's move, I finally just embraced JS/CoffeeScript; I love every bit of it.