The only difference I can see from this site: click here
is The canon pixma photo ip4000 has pigment based black ink. "High-performance 5-color printing. If you're looking for outstanding quality, high speed and advanced convenience features, the Canon Pixma iP4000 Photo Printer is ideal. Its ContrastPLUS 5-color ink system with four dye-based inks plus a pigment-based black ink produces true-life photos with improved color saturation and contrast along with laser-quality text. Plus, it achieves a resolution of up to 4800 x 1200 color dpi*, for exceptional detail and photo-realism."
against the standard ip4000 which just says:
"The PIXMA iP4000 Bubble Jet printer creates vibrant and outstanding image quality, thanks to the ContrastPLUS 5-colour individual ink tank system, 2 picolitre FINE (Full-photolithography Inkjet Nozzle Engineering)technology and 4800 x 1200 dpi."