I do not know, in addition, how often the following conclusion had been made...
I am willing to bet that, if not the entire reason, a major reason they gave Draco this trait is because of something said in book 2, which was not added into the movie. The excerpt begins after Draco asks if his father will buy him a particular something...
"Ah, the Hand of Glory!" said Mr. Borgin, abandoning Mr, Malfoy's list and scurrying over to Draco. "Insert a candle and it gives only light to the holder! Best friend of thieves and plunderers! Your son has fine taste, sir."
"I hope my son will amount to more than a thief or a plunderer, Borgin," said Mr. Malfoy coldly, and Mr. Borgin said quickly, "No offense meant, sir, no offense meant--"
"Though if his grades don't pick up," said Mr. Malfoy, more coldly still, "that may indeed be all he is fit for--" (CoS, page 52)
...I am certainly not one to say that Draco was driven, in the movie, to steal by his fathers lack of faith in him; I would suggest that the movie-makers made Draco a thief because of this portion of the book.
Draco chose the Hand of Glory specifically, after the author gave examples of him browsing through other things, but this is the first item that he actually asked for. He is not a stupid boy, I believe he knew what he was asking for, which leaves me thinking that JKR meant to subtly imply that Draco may have had a tendency to take things he shouldn't have, in spite of the fact that he is wealthy. In that section, thievery in relation to Draco was mentioned three times, which makes in noticeable. Hence, it is my thought that the movie-makers picked up on this, also, and decided to put it to interesting use!
He may need to steal to have everything he wants. In book 1, Draco states, in Madame Malkin's, that he would bully his father into smuggling him in his own broom. Later in the book, there is no talk of Draco having his own broom during the flying lessen--he rides the same thing a everyone else! It is only in book 2 that he asks his father for a racing broom (in just the same chapter as the aforesaid excerpt) and he shows up to school with a Nimbus 2001. Seeing as he's waited a whole year to have that broomstick, he is not as "in charge" or privileged as he makes it seem publicly. Even in GoF, Draco still has the Nimbus 2001--a two year old broom! GASP! Draco-fancy-pants-Malfoy with a less flashy broom stick than Harry Potter? It is my theory that Draco steals (if he steals) because he is spoiled, though not spoiled enough to have every little object he desires from daddy dearest.