The whole "diluting the Force" thing has never been cannonized, it's not a bottle of booze, it doesn't ration itself.
And Revan never got the chance to actually implement the Rule of Two. He came up with the idea, but it was too late to make it so because by then he had a vast following of other Sith and apprentices under him. It was actually Darth Bane that followed the Rule first. It had nothing to do with access to the amount of "Force" available in the universe, but merely the knowledge/teachings of it. By nature the Sith code is doomed to fail with a vast number of followers; that's because a large number of apprentices can gang up on and outnumber a single master, and then make the most powerful of apprentices the new master. This is what is meant by diluting the force, because that one apprentice, although more powerful then the others, is not as powerful or knowledgable then the original master, thus losing any untaught wisdom or knowledge that he posessed forever.
Under the Rule of Two, the apprentice should only challenge their master once all of the said master's knowledge and wisdom has been passed along. If apprentice defeats master one on one then they are worthy of taking that mantle and then starting the process all over again, if they fail though, then they were never worthy of being a Sith in the first place. The Rule of Two simply exhists so the teaching of the dark side can live on at it's fullest possible potential. Darth Revan saw that eventually, but he was betrayed before he could make it so. Read Darth Bane: Path to Destruction, it is the main premise behind the Sith concept, and is actually a very entertaining read.
Okay, nerd rant done, that was fun. I'm going to go flirt with some cute co-workers now.