When a wing stalls the complete wing stalls and the plane stays straight, usually what happens on landing and a tip stalls it usually is caused by adding aileron correction, where one wing tip will drop and quits flying.
Not entirely true.
A well designed wing will start to stall at the root. The stall will propagate along the wing until one of the following: 1) The whole wing stalls. 2) there is not enough elevator authority to hold the aircraft in the stall attitude and the nose drops, beginning stall recovery 3) There is not enough lift generated by the un-stalled wing sections to keep the nose up and the aircraft begins recovery.
So when an aircraft drops a wingtip in a stall it means one of two things. Either, A) the wing was designed in a way that let the wingtip stall early; not good, and is the actual meaning of a tip-stall. Or, B) that the stall has propagated along the entire wing, killing lift and letting the wing drop.
Unless the design is flawed or unfounded, what is happening in most of our aircraft when they drop a wingtip, it's just a stall that has gone far enough to kill the lift along the whole wing.
There are factors that can affect when a wing stalls. Aileron movements change the camber of the wing, effectively altering the angle of attack and stalling of the outer wing panels sooner. P-factor and other prop related turning tendencies can increase wing loading on one side a little more than the other, causing that wing to stall first. (This is one reason full throttle can hurt you in certain aircraft. A big prop spinning up to full speed while the wing is close to stall can change the loading on the wing enough to cause a sudden stall. Most people call this a "tip stall" but in reality it is just one wing stalling first.)
I'm sure there's something I've forgotten to mention.
Edit: I remembered the point I forgot.
If a plane stalls straight ahead it means it's in category 3 above. The wing is no longer generating enough lift to keep the plane in the air, but the entire wing has not stalled yet, the wingtips are still flying and providing stability to the aircraft, allowing to stall straight ahead.