On this particular method, the article says that this is good for making diamond FILMS. My chemistry is a little old these days, but from what I gather, they put a layer of tequila on top of silicone/steel and it forms a coating of diamond on top of it. This would be pretty worthless for jewelry applications, and pretty kickass for that diamond coated saw, sword, or car, ala Knight Rider.
What I've heard about the other diamond creation process mentioned by steel88 is that the lab created diamonds are matches for a certain high grade of diamond. Nature can still create diamonds of a higher grade, which labs are either unwilling or unable to duplicate. This is all just off the top of my head, for what it's worth.