I have not tried this, and was just wondering if it were possible:
Say I have a camera that shoots in 480i, 720i, and 1080i and it's specs say it only goes up 480p or 720p. Why can I not shoot in 1080i and edit and all that in FCP and then use compressor to turn it into 1080p? Is there a loss in quality or any distortion, or could I actually do this and achieve a flawless picture just as if I had originally shot it in 1080p?
If it is not possible to do without any loss of quality, why isn't it?
No, its not possible. Why? Well Tito, you're not taking into consideration the temporal nature of your captured video. Unless you are shooting a completely static scene, each field of an a interlaced frame will differ slightly, as they were recorded at fractionally different moments in time. You can't seamlessly stitch them back together as though they were recorded at the same instant ie a progressive frame capture.
I agree with Andy. You will take a slight hit in quality (depending on horizontal movement) anytime you de-interlace your video.
You can get excellent results with Compressor using Frame Controls (I'm sure there are other excellent tools as well) but the de-interlacing process is still tying or merging 2 interlaced fields into 1 progressive frame. You'll get much better results de-interlacing a corporate video than you will a sports video. If you have lots of action, you would be better off shooting 720p and scaling or up-rezing to fill your 1920x1080 frame.