Why would you want to do that for?
Actually, my question is why would anyone want the WordPress logo there (unless your site is about WP)? Study branding and logos and advertising, one of the first things you’ll learn is to be consistent in your presentation. That logo makes it look as if my site is branded as WP’s site, which it isn’t. *I* own my site, and I’m licensed to use WP in any customized form I wish.
By the way, WP is free and there is no requirement of displaying their logo. WP is intended to be customized for an infinite variety of uses (that is one of the primary attractions of using WP instead of something like Blogger). Many uses are for commercial websites and not for merely personal blogs (sadly this forum presumes that everyone just blogs like a diary). Commercial websites would never want to display someone else’s logo.
Solution: What I did is find the actual .jpg file (right click it and look at the address), and replaced it with my own logo (same size, same filename, same location). This caused my logo to instantly appear. Problem solved! (At least until the next WP upgrade, then you have to do it again).
My feature request (or plugin request) is for WP to offer “Your Logo.jpg” as an option in the Admin.