The rationale behind sticking with XP is simple: it allows us to use our PCs as they are (a mix of laptops and desktops). On our 5-year-old machines WinXP runs ok, whereas Win7 would crawl instead.
Also, add the cost of reinstalling ALL our programs and reconfiguring the machines... We simply cannot afford such a cost right now. I hear many smaller companies are in the same situation. There's a double-dip recession out there ya'know?