Cliftor: Virtually all CD checks, even from "older" games WERE Safedisc and such. These companies sell all sorts of copy protection kits, and for the longest time it was just a CD check included in the maingame.exe.
It's not that they sell various different types of copy protection, it's that the code has been upgraded and gotten new versions like any program, now most of them contain a host of different optional parts that the developer/distributor can chose between as they see fit, earlier versions of them maybe just had the serial key and/or cd check, so that's what was used. Nowadays most has optional parts of online checking, disc check, serial key, number-of-installations, and maybe other things as well, and they do it through different means; installed drivers (hidden or visible), code directly in game exe or in external dll files, extra programs that need to be installed (ie. Steam)... you name it.
Just like you can chose to install only the parts of an application that you want (for those that has an option of custom installation), developers can chose which parts of securom, tages, et al. they want to use.
Like any software developer the copy protection developing companies need to create new versions of their software to be compatible with modern systems and add features so that their customers want to keep buying from them instead of their competitor. Why do you think Microsoft has been releasing new versions of Windows and Word every few years? Why have they been modifying them and adding features? Why did they not continue the GUI-on-top-of-DOS Windows after Windows Me but instead only continued with the NT line as they released XP, and why did Apple scrap their Mac OS and decide to go with a Unix base after OS 9? Same reasoning applies to copy protection.
Bah I've ranted far too long, and this post is largely totally unnecessary, but I don't want to having typed all this just to click "cancel", so here you go.