Sony Fontopia Headphones: 71SL vs 51LP

quick question:

does anyone know the difference between the Sony MDR-EX71SL and [url=http://www.sonystyle.com/is-bin/INTERSHOP.enfinity/eCS/Store/en/-/USD/SY_DisplayProductInformation-Start?ProductSKU=MDREX51LP&Dept=audio&CategoryName=pa_PADepartmentAccessories_Headphones_Fontopia%2e%2fEarbud]the MDR-EX51LP?

The only difference I can find is that one has 3 different earbud sizes while the other only has 2. However, the price differs by $10…10 bucks just for an extra ear size?