The update center's "Updates" view positions the buttons to select "All", "Compatible" and "None" plugins at the bottom of the page, like the download button to download the selected plugins.

If you take a look at the "Available" view, you can see a bottom bar following your scrollbehavior to download the selected plugins at any time without scrolling to a specific location of the page.

I attached a screenshot how a proposal for a bottom bar for the "Updates" view could look like. This would come in handy when you're updating more than just a few plugins and don't want to scroll back and forth to use the buttons.