Your correct to a large extent, the "bending" comes from the tool joint when drilling, the BHA (Bottom Hole Assembly) is made up of Drill collars that are a lot heavier than the drill pipe, these days most directional drilling is done with motors, but traditionally when rotary drilling adding shorter components to the BHA, which gives more tool joints which gives more "bending" capability.
All tubular s that are used for drilling are inspected, there are comprehensive inspection procedures in place as failure can be Very expensive.
Example below:- probably not the greatest explanation!