I've added some clarity about my observations of St Michael logo design changes to the label thread: http://www.forums.vintagefashionguild.org/viewthread.php?tid=44330&page=2
My thought about reason for the size of "leather uppers", was that it's because M&S shoes are sold exclusively in M&S stores, and only M&S products are sold in M&S stores. They don't have shout their own brand here - if you are looking at the shoe you're already in their shop, and all the shoes you are looking at are by M&S. So it's more important to highlight the features of this particular shoe, than the brand name.
My thought about reason for the size of "leather uppers", was that it's because M&S shoes are sold exclusively in M&S stores, and only M&S products are sold in M&S stores. They don't have shout their own brand here - if you are looking at the shoe you're already in their shop, and all the shoes you are looking at are by M&S. So it's more important to highlight the features of this particular shoe, than the brand name.