Combining Typefaces

Smashing Magazine has just released an article on combining typefaces.

Whilst this is a great primer on the differences between typefaces, I can't understand why they have chosen to use different font/background colours for the left and right panels on each comparison, not to mention the use of drop-shadow and/or engraving not only on the fonts, but using them differently on the left and right panels.

Maybe Douglas Bonneville is more designer than scientist, but if you want to make a comparison based on just one thing (in this case fonts), you should ensure that when showing side-by-side examples that they only vary by this one thing. Especially as all the 'negative' examples are shown using dark backgrounds and white fonts with drop-shadows.