I think it ironic that VM gets stats far closer to what they promise than any other ISP yet comes off so relatively badly in customer surveys. As has been said VM customers have even higher expectations.
The technology ensures that the equivalent of the sync rate will be what was sold unless there was an error of some sort. ADSL is highly dependent on the phone line and the public are by and large too poorly informed to properly understand that.
VM's practice of no pre-emptive capacity upgrades ensures that a percentage of their customers will be getting pretty abysmal performance at peak times and sometimes beyond. Their tardy resolution of such issues alongside that ensures a high level of complaints - the majority who get what they were sold are for the most part silent. Selling high headline speed products on marginal infrastructure makes it possible for a single heavy downloader/uploader to have an adverse impact on his neighbours doesn't help either - on ADSL a single service abuser won't impact anybody.
Using low quality offshore support who appear to follow a strict script and then invent complete BS when the script runs out ensures poor TS ratings.