Operating Systems - lost it's importance?

Since MS-DOS came in to the market, Microsoft was monoploy in the inexpensive operating system market. Recently, Mac & Linux have come in the mix. Mac on the desktop market and Linux in the server market.

Thrown in to the mix is Virtualization (Desktop) and Cloud (Server). Now, is it time to preciously define what is Operating System and see if it is still relevant? May be we do not need Operating System after all. May be a dumb terminal connecting to various specialized applications on private/public cloud could be one of the path?