OBDII tools/scanners; why are they limited to PCM codes?

Since all the data is on one bus and one connector, why are all these under $600 scanners only able to monitor PCM codes? Why is there such a difference in price (5 to 10x) between these and the full testers the factory shops use?

Yes, I understand there is more involved, but since the data is there on the same connection, what's the big deal to display all the codes? I would understand if it involved another connection and/or a different data bus logic, but it's all the same, isn't it? Just ones and zeros as in a computer.

each manufacturer does it differently, and every model is a little different. It takes a lot of effort for the scanner makers to figure out the data streams, and a lot of it is propriotory. Manufacturers don't give out that kind of info

If they have the info for the PCM, what's the big deal for the other modules?

I just said it. OBD2 is universal. nothing else is.

scangauge?

it's not just about being universal man. Kuz OBDII isn't really universal. Each manufacturer has a different adapter for OBDII and a different bus. When you make a scanner do more than just read OBDII codes, then you'll need to make it comply with every car's standard, which gives you alot more combinations than just reading OBDII codes. Think of this...Real scanners have the ability to turn on and off the fuel pump. Now imagine having to program that for 100 different models (some cars can do it, some cant).

it's not just about being universal man. Kuz OBDII isn't really universal.

err...yes it is. There's been 4 or so protocols created for it so far, but the manufacturers all must comply with the protocol of the day, and the protocols are open for all to read, code and use. Its not propriotory like anything else you'd like to do with the data stream coming from a car

All cars have 2 ECU's rolled into one. One side is purely for the OBD2 part, the other part is the manufacturers ECU