A lot of those treatments for dementia have been shown to improve cognitive performance in normal people as well, so I can't complain too much.
Namenda and Aricept: 2 of the most widely used drugs to treat Dementia and Alzheimer's. Your statement is only partly true. Only a low percentage benefit (about 10-20% I believe of severe late stage cases) benefit from them. --> most recent study http://www.cnn.com/2011/HEALTH/04/11/alzheimer.drug.ineffective/index.html
I pass these meds out all the time to patients. It barely makes a noticeable improvement from my own experience, but I have also seen some rare cases where a patient was taken off the drug treatment (due to family unable to afford it) and cognitive and level of consciousness took a nosedive.
For the majority of patients, these drugs only mask the symptoms and come with some nasty side effects. We got a long way to go imo from finding any kind of breakthrough.
I hope I'm wrong because its one of the worst diseases to get because how it emotionally affects family and loved ones.