In late 2006 a target exclusive 2 pack arose. Skywarp, a repaint of Starscream, and Ultra Magnus, a white repaint of Optimus Prime.
This was a shelfwamer for a long while, because not very many people wanted to get a white Optimus Prime toy, rather most fans waited until it went on clearance and even then only bought it for the Seeker mold.
This was a mistake. FansProject released the City Commander add on set just a short while later. Because of the Ultra Magnus toy not selling as well or rapidly as fans may wish they have, the price on aftermarkets skyrocketed. With the Add on selling incredibly well and the fact that the other colorations of the Optimus Prime mold being more readily available, there were more repaints of the armor.
This was followed by the trailers made for the classics Optimus Prime mold based on its sales. So, with a wide array of toys made for this mold, a disambiguation page was a neccessity.
And now we've come full circle.