The basic distinction is between full-time and part-time 4wd.
Older jeeps have part time 4wd and when engaged (must be on a surface that allows some wheel slip), forces the front and rear AXLES to turn at the same speed. Effectively there is a 'locked' centre diff. However individual wheels on each axle can still turn at different speeds, hence being stuck in off road situations that lead to one front and one rear wheel in the air spinning but no forward movement. The individual diffs on each axle are 'open' if the above happens. A limited slip diff (often an option or standard on larger 4wds and only on the rear!) helps prevent getting stuck by limiting different wheel speeds across an axle. I think you are confused with diff locks, usually an expensive aftermarket option (ocassionally a factory option)that does lock individual axle diffs forcing both wheels on an axle to rotate at the same speed.
The RAV4 always has an open front axle diff and an option of a rear axle limited slip diff (not a diff lock). The centre diff is open most of the time (hard surfaces) as in all constant 4wd cars. In manual trans RAVs it can be locked for off road use, in efeect converting it to 'part-time' 4wd. You may need extra accelarator when turning. On auto trans RAVs the centre diff is as you say. I am not aware of aftermarket axle diff locks for RAVs, there is certainly no factory option.