The rule about misleading advertising applies to any company. The comparison about 150kbps has nothing whatsoever to do with it. The regulator has defined that 150k IS broadband. If you don't like that decision then complain to the regulator. The ASA has stated that Onspeed have created a misleading advert. If you don't like that decision either then write to the ASA and tell them.
I don't care that Onspeed explain on their website that what they are selling isn't Broadband. It's not up to the customer to find out that the company are misleading people through their advertising.
If an advertisement tells me that I can buy a service for £2 a month that will give me something that I currently pay £30 a month for then that is not only misleading it's a downright lie. All advertisers and magazine publishers have a duty of care not to carry misleading and false advertising and I expect both Onspeed and WU to abide by the law.