The answer to your original question is, there are inserts and there are holders- some work together, some don't. It's an a'la carte system. I think David's book is a great collected reference, and will no doubt help you decode the system.
I find it a little too expensive to buy any type of insert cutter without making darn sure the inserts are common, available, and cheap first. It's just my luck to pay $10 for a $200 tool holder, but Sandvik makes the only inserts at $200/box. I prefer the simple approach, I can get CCMT inserts (for example) cheap, so let's choose a holder that uses those over something less ubiquitous. I have a couple nice Kennametal boring bars, but they use proprietary "ridge top" inserts that are $20 each, so those bars aren't very useful. It's a long row to hoe when setting up insert tooling if you don't pick a couple workhorse insert types early and stick with them.