Sunscorch - yes there are some unscrupulous therapists but I'm not sure you will find many Reiki practitioner with private jets!
There is actually a legal code of practice for complimentary therapists so they are not/and should not be claiming that they can cure cancer or perform miracles etc.
With Reiki specifically as I have said in earlier posts it works in the best interest of that person and soul. It could that it is the persons time to go and so Reiki will them work to ease the passing - it is not sold as a cure all.
Modern medicine is great but it still can't cure everything can it? I mean there are obviously the big diseases such as cancer and AIDS that don't have a cure but there are also many smaller diseases that don't have a cure either such as PMT, Migraines, IBS, infertility etc so I don't think that modern medicine is the solution to everything.
However with some of these illnesses Reiki can either fill the gaps in modern medicine i.e provide help with fertility if IVF doesn't work or it can support the moden medicine i.e. helping to give energy to someone undergoing chemo.
Personally I see Reiki as "complementary" rather than "alternative".
I don't really think that you can compare Reiki practitioners to the pastors of mega churches on megabucks. Most Reiki sessions cost between £20-£40 depending on area - so not an extortionate ammount but people do get alot out of it.