Many extensions and web apps in google chrome use background pages in order to carry out their functions. The main reason for this is background pages and background apps which keeps on running even when you close the google chrome window.
There is simple reason why you see chrome.exe running even after killing google chrome and quitting it. There are some users of google chrome who reported that when they exit google chrome by clicking the red cross button at the right top of the browser, as these google chrome users noticed chrome.exe running when they open task manager in windows.
