My 2c:

Pau's concern seems valid, in a sense that stream should work like TCP.
That's what most users would assume -- read out data until the end, only then you can see what the actual error was (socket closed, or timeout or hard error)

However, I suspect the devil may be in details -- the patch appears to assume that exception is only set by the underlying source of data (in which case user wants to read out everything up to the exception).

I can imagine a couple of use-case where an exception is set "out of band":
* to terminate bad reader (e.g. against Slowris attack)
* there's a matching StreamWriter (e.g. shared socket)

P.S.
If I'm wrong here, then bug report and patch must be clearer :)