Nokia is often cited as a big contributor because they bought TrollTech. Much of Nokia's own work on WebKit for the S60 never got merged back into the mainline.

Nokia is often cited as a big contributor because they bought TrollTech. Much of Nokia's own work on WebKit for the S60 never got merged back into the mainline. Similarly, RIM's contributions were actually Torch Mobile, who they acquired less than two years ago. Torch employed several long-time KHTML and WebKit contributors. Google are (I believe) the biggest single contributor today, but their contributions aren't yet substantial overall. Apple's contributions included extensive work on standards compliance, web compatibility, performance, security, robustness, testing infrastructure and butt loads of major features. You know, the important bits.