However, a new full specifications listing on Ubisoft's Uplay store reveals that in fact it does require a 64-bit OS. The 'leaked' specs were also pretty accurate to these new more official ones.
The minimum RAM requirement has actually bumped from 4GB to 6GB in the new list, although no 'Ultra' setting specs have been released.
Supported OS: Windows Vista SP2 64bit, Windows 7 SP1 64bit, Windows 8 64bit
Processor: Intel Core 2 Quad Q8400 @ 2.66Ghz or AMD Phenom II X4 940 @ 3.0Ghz
RAM: 6 GB
Video Card: 1024 VRAM DirectX 11 with Shader Model 5.0
Sound Card: DirectX 9 compatible Sound Card
This product supports 64-bit operating systems ONLY.
Processor: Core i7 3770 @ 3.5Ghz or AMD FX-8350 @ 4.0Ghz
RAM: 8 GB
Video Card: 2048 VRAM DirectX 11 with Shader Model 5.0 or higher
Sound Card: Surround Sound 5.1 capable sound card
Supported video cards at time of release:
nVidia GeForce GTX460 or better, GT500, GT600, GT700 series
AMD Radeon HD5850 or better, HD6000, HD7000, R7 and R9 series
Intel Iris Pro HD 5200.
Watch Dogs releases on PC, Xbox 360 and PS3 November 22nd.