Some features, like SPDY, can be implemented even though not all the browsers support it -- which means that those that don't will find that their users think their browser is slow.
Some features can be emulated with things like long-polling.
And some (WebGL) can't.
I doubt you will be right about those features that can be replaced or emulated but you are properly right about those that can't.
Then again every day we choose to exclude some customers (you only speak Japanese? Well sorry then).
I doubt many sites are going to bother with all the complexity of implementing and utilizing SPDY when only chrome supports it. To see significant advantage with SPDY vs something like long-polling you need to build your app around it, and if you need to support long-polling methods anyways, not very many sites are going to bother.
I think you are confusing SPDY[1] with WebSockets[2]. SPDY is Google's experimental replacement for HTTP. You don't build your app around it at all - from the application layer it should be mostly invisible.
SPDY can be implemented as an Apache module[3] which could be used only when the browser supports it.
It is true that WebSockets replace long polling, but there are plenty of libraries that abstract the differences out nicely.
Some features, like SPDY, can be implemented even though not all the browsers support it -- which means that those that don't will find that their users think their browser is slow.
Some features can be emulated with things like long-polling.
And some (WebGL) can't.
I doubt you will be right about those features that can be replaced or emulated but you are properly right about those that can't.
Then again every day we choose to exclude some customers (you only speak Japanese? Well sorry then).