A sheltie is not a mini collie because it is simply not a collie in miniature. Unlike a miniature poodle, we did not get a sheltie by breeding small collies over and over until we got a desired size of between 13 and 16 inches.
A quote from wikipedia- "Unlike many miniature breeds that resemble their larger counterparts, this breed was not developed simply by selectively breeding the Rough Collie for smaller and smaller size. The original sheepdog of Shetland was a Spitz-type dog, probably similar to the modern Icelandic sheepdog. This dog was crossed with mainland working collies brought to the islands,[6] and then after being brought to England, it was further extensively crossed with the Rough Collie, and other breeds including some or all of the extinct Greenland Yakki, the King Charles Spaniel (not the Cavalier), the Pomeranian, and possibly the Border Collie. The original Spitz-type working sheepdog of Shetland is now extinct, having been replaced for herding there by the Border Collie."
A collie has a much different and longer history, going back to the 18th century
http://www.collieclubofamerica.org/breed_history.html.
I'm starting to feel like no matter what, you're never going to be satisfied with any answers we provide.. maybe if you specified what you're looking for? You've gotten quite a few good answers here...