In 7D
technically, in Crop Mode its recording a "cropped" portion of the sensor.
However, in 1X, when you change resolution for example from 1728 width to 1280 you will see your framing guide white rec reduce in size poroprtionally thus recording only a "cropped" portion from that of 1728, so yeah, its still cropped with line skipping while 3X crop does not employ line skipping, thats the difference I guess.