I believe it is true, the difficulty is that to date none of them have been caught, primarily because the authorities have not tried. If you look at retail forex however you will see that many companies have been caught defrauding their clients using some of the methods you mention. They have all been caught by the US authorities though, as SB is not allowed in the US the SB companies get much less scrutiny than would otherwise be the case.
lets put it into context.....
take the TBTFs & other multimstionals' nefarious activities of late which have at least been fined: libor fixing (Barclays); swap rate fixing (JPM); electricity price fixing (JPM et al); oil swap price fixing (Total); martingaling when supposed to be a hedging risk function (jpm - the whale); using client fund as collateral to leverage trade sovereign bonds (MF Global); Money laundering for mexican cartels (HSBC); equities (everyone Buffet etc)
so out of major mkts this only really leaves gold (PMs - wont be long before this gets found out) and fx - which are not being manipulated (haha). regulating fx wld be a nice start.
(must have missed some off, anyone got anymore? i have only been adding one example so if you have anymore)
so with these fine custodians what do you expect further down the chain? its a morally bankrupt industry, & i worked in it for far too long.