The difference between Franz Ferdinand and AC/DC is that AC/DC's riffs never seems to get stale.
Ding! Which is why I have about 10 hours of AC/DC in my collection, and only 45 minutes of Franzizzle Ferdinizzle.
And I'm totally not buying there only being a gradual change in the music of say, The Beatles or The Beach Boys, that's total hossshit. The difference between Yesterday and Helter Skelter is not gradual, it is radical. The difference between singing about surfing over Chuck Berry riffs and making music that was at the vanguard of American psychedelia at the time is not gradual. I get the point you're trying to make, but those aren't good examples.
There is a lot on The Darkness' second album that sounds like the first, they were just unafraid to experiment with different instrumentation, which is how you develop as an artist. Like when Pete Townshend programmed Meher Baba and Terry Riley's vital statistics into an ARP synthesizer to create Baba O'Riley. Although of course there's no difference between that and, say, Substitute.