Ok, let's clear up a few things
"PAL" - which isn't actually the correct way to refer to the system - runs at 25fps, not 24. Film runs at 24. "NTSC" (also incorrect) runs at approximately 29.97.
"Scan rate" is the correct term for the above numbers, although technically the scan rate is the field rate, not the frame rate. There are two fields per frame, so the scan rates are 50 for "PAL" and 59.94 for "NTSC". What you're thinking of is the vertical resolution of the picture, which is 625 lines (575 visible) and 525 lines (480 visible) respectively.
To be absolutely accurate, the two systems are referred to as "625/50" and "525/60". Most countries use 625/50; the main exceptions are the US, Canada and Japan. Colour system is a matter of choice: most 525/60 countries use NTSC (Brazil, on the other hand, uses PAL) and most 625/50 countries use PAL (but France uses SECAM). This being the case, it's common to abbreviate to just saying "NTSC" or "PAL", but it's not strictly accurate.
The vast majority of DVD players sold in 625/50 countries will also play 525/60 discs. In theory, the opposite is also true, but since this relies on your TV set being able to handle the "foreign" signal, it's not that common in the US. There are two types of US-sold DVD player capable of handling 625/50 discs: those that require the TV to be able to handle the signal, and those (more expensive ones) that actually convert the signal to 525/60 internally, and will work with a normal US television. You're always better off with the first type, as any standards-conversion introduces nasty motion artefacts and other problems, and the convertors built into consumer players are pretty basic (unless you want to spend really big bucks!).
Region coding was indeed introduced to control when and where a title was released. Hollywood films are typically released first in the US, and then to other countries a few weeks or months later. Since the distributors in these countries are purchasing exclusive exploitation rights to the movie, the last thing they want is for Joe Public to be able to stroll down to their high-street DVD store and buy the thing before it's even opened in the local cinema. It's merely a side-effect that region coding allows the studios to screw their customers over... ;-)
"RCE" is nothing new; it's been around for many years. It's a fairly simple trick, and usually fairly simple to defeat with a modified player. Most "region-free" mods will also disable RCE.