I'm a bit fuzzy on the logic but I think it has more to do with little modifying old lady, while both tall and slender modify lady. In other words, old and lady are so closely associated that they *are the noun. Likewise, I would not use a comma with large brown dog. I'm not explaining this very well; need to find a punctuation guide that (1) agrees with me and (2) clarifies why.


EDIT: This - http://snipurl.com/a0nm - helps some; scroll down to #6 and continue with #1 under Misusing Commas.