It's easy to criticize those taking Apple to court, as most people know better than to believe what you see in a commercial word for word. In Apple's case, however, it isn't just individuals who are getting involved and finding fault with what Apple does – cases in both the UK and US have resulted in the courts ruling against the company and even forcing them to remake one of their advertisements. Which is ultimately what’s at the heart of all these cases: people are not suing over what speeds they get, but rather what they believe Apple told them they could.
Apple has faced down numerous lawsuits in the past revolving around this same issue. Perhaps they feel that the cost of dealing with these lawsuits is less than the potential customers they might lose if they don't promise unrealistic speeds.