why MF_MT_FRAME_RATE_RANGE_MIN and MF_MT_FRAME_RATE_RANGE_MAX are equal?

I'm writing a simple program to pull every frame from a webcam, but I found these codes

MFGetAttributeRatio(pType, MF_MT_FRAME_RATE_RANGE_MIN, &w, &h);
MFGetAttributeRatio(pType, MF_MT_FRAME_RATE_RANGE_MAX, &w, &h);
MFGetAttributeSize(pType, MF_MT_FRAME_SIZE, &w, &h);