No, the switch has not always been keyed to a new Doctor; Tom Baker served so long as the 4th incarnation that he spanned two title designs. Peter Davison‘s and Colin Baker‘s fifth and sixth Time Lords also shared Tom’s second, “neon” logo, while the 9th and 10th both employed the 10th, the current oblate-spheroid look.
I have to say I like the new look. But perhaps that’s more because I never really liked the current logo, which came along when the series was reimagined in 2005. I loved (and still love!) everything else about the relaunch, but the stretched-out, flattened, yellow-orange graphic just never clicked with me. Perhaps that’s why the blockier, more solid design appeals to me. I also like adding the TARDIS lamp on top and creating “official” alternate looks, including an abbreviation that mimics the shape of the TARDIS itself.
A new logo, new show-runner (Peter Moffat), new Doctor (Matt Smith) new companion (Karen Gillan) and even a new sonic screwdriver (!) make the show seem new again in a wonderful way. I just hope the rumor that the new season will again be designated “Series 1” proves false. It should be referred to as “Series 5.” Actually I have been hoping that fan-made-good Moffat will be the kind of traditionalist who might revert to the “proper” original numbering – which would make the new series Season 32. (That’s how I think of it, anyway.) Hope regenerates.