On terms of responsiveness i can only tell: it depends on your computer.
if your computer is well configured - yes it will beat the hell out of a cloud app with html.
But cloud computing enables you do a lot of shit behind the sense that improves responsiveness.
For example:
usually it is faster for me to start chrome type gmail and check my e-mail, than it is start thunderbird / apple mail and check my e-mail.
so for my crappy computer: cloud computing is faster !
e-mail search is also better. I actually disabled e-mail indexing for my e-mail desktop app, because it slows down my computer big time.
Gmail indexes don't eat any performance on my end. Cloud computing is again faster.
And if I switch my computer, it will take me at least an hour to setup all my e-mail accounts. With gmail i can just start.
And i can check my e-mail on my mom computer.
And that is just the e-mail use case for me as single e-mail user. And I'm actually not a computer noob .
Now, think about a systems administrator. With cloud computing he can safe himself a lot of headaches.
Of course, cloud computing will not come free of problems, but any problem you solve you solve for the entire user base of your business.
That's why cloud computing is so important for a lot of people. It is hardly new. For example, mainframes are similar to cloud computing.
So this general concept of moving stuff to the big fat ass server is not new. However, the implementation and several other details make it useful for this generation of computer users.