It's not like Back/Forward browser buttons are overrode to behave and previous/next for the slide presentation.
Remember those horrible embedded Flash presentations that you couldn't directly link to a particular slide within the blob? Yeah, that "breaks the Web". Back/Forward is supposed to go back to the previous page the user was on (which is a "slide" in this case).
Using Chrome 43.0.2357.81 (64-bit) / OS X.
In the scrolling case, I still don't see how it's "overriding the browser buttons", but rather having a JavaScript that advances to the next page on scroll.
In the scrolling scenario, my actual back and forward browser buttons behaved as expected — just for the pages (slides) I visited. No more, no less.
Going to a new tab in Chrome, navigating to <https://docs.google.com/presentation/d/1r7QXGYOLCh4fcUq0jDdD..., and clicking my browser's "back" button takes me back to the New Tab Page, so I'm not sure I'm seeing the behaviour you're describing.
There should be a "share" button that spites out the URL with the hash-tag of the current slide - similar to Youtube where you can click on the "share" button below the video to link to a specific time in the video, e.g. https://youtu.be/I26EwcssMbY?t=1m37s
If you find yourself having to interact with these a lot, which I do, you might find it useful to click on the cogwheel icon at the bottom of the screen and select 'Open in editor'. That gives you a completely different and IMO much easier to read view of the same document:
https://docs.google.com/presentation/d/1r7QXGYOLCh4fcUq0jDdD...
You could argue that every link should open in a new tab by default and only replace the contents of the current tab in special cases, instead of the other way around. In the past 20 years we've been 'trained' to have different expectations, because of the design of the first websites, browsers and the resource limitations of those days. However, the designs and abilities of all of those have changed and it may be worthwhile to reconsider the current default.