Simon Singh is in a tough position because he spoke the truth. Simon was sued for libel by the British Chiropractic Association for claiming that some of their treatments are bogus (which they are).
In the first round of the lawsuit, a judge sided with the BCA regarding the use of "bogus" and suggested that Simon meant that members of the BCA were being dishonest - Simon was only suggesting that members of the BCA are promoting treatments that, themselves, have no scientific basis (bogus).
I would suggest that there are likely - like the priests/pastors who don't believe the sh*t they spew - a number of chiropractors that are knowingly and willfully being dishonest - even though Simon didn't say that.
Having said all of that, the courts ruled against Simon and, normally, it is advised that the defendant would pay the costs and accept defeat - it isn't often that a ruling like this is overturned and it would be difficult for Simon to now defend that interpretation in court (if the judge, however, interpreted the article the way it was actually written, Simon would only be attending court to say "these treatments are bogus and here is the evidence") - he would not be able to prove that members of the BCA (or the BCA itself) was consciously advocating/promoting bogus treatments - which the judges ruling would have required him to do.
The Guardian newspaper offered to pay the costs of the BCA and the other resulting costs of Simon based on their legal advice to accept defeat and move on. The cost to appeal and appeal and appeal could be substantial and the truth of the whole situation is not a disproving of Simon's claims but would be heralded, I'm sure, by the BCA as a victory and "proof" that they don't promote bogus treatments.
Simon Singh is doing something that takes balls, he's appealing the decision. Simon would be happy to attend court to PROVE that certain chiropractic treatments are IN FACT bogus. His appeal will, possibly, give him the opportunity to do just that - and defend his statements as they were written and intended to be read. It would be a wonderful day for all skeptics to see the BCA attempting to defend their treatments in a court of law - the proof is overwhelming that many of their treatments are completely pseudoscience (woo-woo).
For more information, Jack of Kent's blog is a great source. (This link specifically talks about a push for change in libel laws to stop the suppression of skepticism but does have much information on the Simon Singh case.)
Thank you Simon and all others who are fighting for the right to be skeptical and present evidence for/against claims. The truth is worth it.