I'm not an expert either, but I think it's all down to the volume of traffic flowing in and out of the ISP's server. Bit like oil down a pipe ... Paddy has a medium size pipe, but 'cos so much oil wants to flow down it, he's gona need a bigger pipe.
As was pointed out, no photos are hosted on the VOD (and it's these that can be quite large files), so the volume of information transfer to build a page shouldn't really be that great.
Either there is a massive number of people requesting information from the server, or due to old software it takes a large volume of info to make a page or there's a problem like a virus consuming bandwidth.
Only the ramblings of an idiot ... I'm sure someone else can explain it better.