What do you think Printer companies make more money on? The one time $50-$100 printer purchase or the $10-$40 ink that has to constantly be replaced?
In the past when a color was "out" the printer would not know and just print as if it had the ink. But when the printer prices started to fall, you can get some for as low as $20-$30 on sale, the companies had to do something.
So just about every major company puts in features in at least some of their printers that will not print if any cartridge is below a certain level. Some even "know" if you tried to refill the cartridge and will force you to buy a new one. A "general" rule is that the more expensive the printer the cheaper it costs(on a price per page basis) to replace the cartridges and the more "lienient" the printer is in this.
The one advantage that your printer has over some others is that you have separate cartridges for each color. Some combine the 3 main colors(Cyan,Majenta,Yellow) into tri-color cartridge. So if you use one color you still end up replacing all 3, in your case you only need to replace the one that is out.