Is your firm like shampoo?  In this post from his Confessions of a Brand Evangelist, Aaron Dignan talks about hair, dandruff, and the commoditization of clean:

The funny thing about shampoo though, is that cleaning hair is its purpose, and yet almost every shampoo brand on the planet is building a story around something else.  Head and Shoulders fights dandruff.  Nioxin stimulates the scalp and fights hair loss.  Brilliant Brunette by John Frieda keeps those lovely espresso tones in your hair going strong.  Nobody's talking about cleaner hair.

Why?  Because the purpose of the category has been commoditized.  Everybody's shampoo works, so they've changed the discussion.  My guess is that if you look at your category, you'll find that it's more like shampoo than you'd like to admit.  Everybody's stuff works.  The real question now is: what's the something extra that you're going to talk about on the side of the bottle?

So, even though you may think you have a “distinctive global law firm with a diversified practice that offers a broad range of services and has become a leader in every area of law you practice because of your client focus and legal skill,” you still need to articulate that “something extra” on the side of the bottle. 

If you think I’m wrong here, go to your bathroom and look at your shampoo.  Unless you are using a generic no-name brand that just says “SHAMPOO” on the bottle, you’ve looked for that “something extra” the last time you went to the store.  What makes you think your potential clients won’t as well?