Why were item outdated?

Wernham-Hogg were obviously making cutbacks when the mockumentary was set in 2001 hence the merger of the Slough and Swindon offices. Maybe they had been trying to save money for a few years in other areas such as not upgrading to the latest office equipment until it was really necessary.

I think a lot of the material was written in 1998. There's even....not quite a "pilot" - I'd call it more of a prototype that I've seen on youtube, not sure if it's still available. It mostly focuses on Brent, the temp and Dawn (only Dawn's played by someone else) and that whole "fake firing" scene is done. There's some voiceover narration too which would be more consistent with a docu-soap.
Flat Eric, the George Michael jokes, the fact that Dawn's talking about school re-unions (by the time it aired I think friends re-united would have been fairly popular) and as already stated, the outdated technology, plus docu-soaps were everywhere in 1998. By 2001 they were being replaced by reality shows (big brother being out the year before).
The only thing in the show to suggest it's more recent is the music when they're in the club.