If the players are turning consistently to their rulebooks when they are together in person, then it probably would be a good idea for them to place bookmarks throughout their rulebooks so that they won't waste time flipping through them to find whatever it is they are looking for.
PDFs of the rulebooks with bookmarked links can also reduce the amount of time that is wasted trying to find a particular rule.
Lastly, this problem IMO is probably common with players who are relatively new to the game and the rulebooks. If you have been playing in a RPG for years, you already have a good idea on what's in the rules.

And you probably already have a good imagination to boot.