Confused with image uploading on different spots...

Okay, there are certain spots where I can do 'unlimited uploads' but there are also spots where I can only upload '20 imagens at a time'. What's up with this? How can there be any difference when it comes to image uploading? & why can circumstances be different on several spots?

For instance, I can do unlimited uploads on the "Pink" & "Madonna" spots. However, On the "Cheryl Cole" & "Selena Gomez" spot, I could only upload 20 imagens at a time.

Would anyone care to answer?