Yes, the DEA is absolutely playing politics. Citizens should expect no less from a government agency. When there is documented evidence of medical use for marijuana, for an agency to deny that means they have an ulterior motive. Their fears of marijuana getting out of control may be founded, but it's no reason to lie about the drug.
The DEA is playing politics by not recognizing the medical benefits of marijuana for some illnesses. Unfortunately, the DEA has chosen to continue the government's failed war on drugs. A war which has resulted in the incarceration of millions of non-violent drug offenders over the past 40+ years - turning many non-violent people into hardened criminals. The DEA should decriminalize marijuana so that fewer people end up in prison.
It is not the DEA's place to render an opinion on the efficiency or lack of medical benefit of drugs. They are not set up to conduct medical research. Also, the largest growing drug problem in the United States if from legal prescription drugs that are being misused or abused.
There are noteworthy articles published in high-profile journals suggesting that marijuana may help alleviate the symptoms of certain disease. Keeping medical marijuana illegal may give the DEA an additional substance to target; if it is made legal, less penalties may be given for its use, earning the department less funds.