Just so you understand what i'm talking about, here is a regular plug without those "slits" (I don't know what to call them):
And here is a plug with them:
I only noticed this diefference because my phone (Samsung Galaxy s2+) doesn't work very well with the first kind. What makes things difficult is that nobody seems to know about this - not my friends, not the clerk at the store, no one - so it makes it hard to buy the correct micro-USB cables that will work with my phone.
So - what is the deal here? Are those things just something that some manufacturers decided to add to their products? (The official USB diagrams don't show the slits).