A Good Question.
Answer One - Sound Quality
When an analogue (Non-Digital) recording is made, all nuances of the sound are recorded. In the transfer process to Vinyl, none of the recorded information is lost. What you hear is a full faithful rendition of the actual recording.
When a recording is digitised to master it for a CD release, approximately 90% of the information is discarded. This information is the nuances which fall outside the range of human hearing (so they claim), but it is very apparent when listening to the same recordings on CD and Vinyl (on a decent system) that the lost information is not inaudible and there is a distinct loss of texture and warmth. So CDs are noticably inferior to Vinyl on a decent system. On an average system, you probably won't be able to tell the difference.
A typical 50 minute CD album uses about 500MB.
Ok - so now we get to downloads. The file size for a typical 50 Minute CD Album download is currently about 50 MB in standard MP3 format. So suddenly we've lost another 90% of the information on the CD, which had already lost 90% of the Vinyl information. So your average MP3 contains only 1% of the information recorded. If you are listening on cheap headphones or in the car, then you probably won't notice the difference. If you are listening on even an average system, the MP3 will sound cold, sharp and lacking in depth and resonance.
Answer Two - Artefact
An Album is a piece of Art. Intrinsically, it combines Music and Sleeve Artwork. Whilst many have tried to deliver CDs in strange packages, there is nothing that comes close to holding a 12" by 12" work of art as part of the experience of listening to music. CDs are 5" by 5" and the impact of the artwork is correspondingly lessened. It's like looking at the Mona Lisa on your Iphone. Mp3s have no artwork, so draw your own conclusions...
Somehow, the 12" Album format captured the best way to experience music - if you've never put the needle on the record, you should try it...
ps - 7" Singles are just cool anyway...