Most of them have some "boss" who is collecting all the money, and giving them just a bit of it. So instead of giving them money, it's much better to buy them food or something else what they really need.
That's interesting, if it's true. Do you have a source?
Couldn't really find great english articles about this phenomenon so I don't know how reliable these sources are, the local media usually calls it "begging mafia" or "organised begging":
- A paper dealing with this topic: http://webs.schule.at/website/Texte_online/Organized_Begging...
- http://www.neurope.eu/article/slovak-clans-control-organised...
- http://www.viennareview.net/news/austria/end-station-for-u-b...
- http://viennatimes.at/news/General_News/2010-09-06/25437/Beg...