When it comes down to it, emulators are legal as long as the bios is not provided with the package. Roms on the other head, are illegal to download unless you have a legal copy and/or ripped the rom out yourself. Now, why would google start to remove those emulators? The main reason would probably be legal pressure from the gaming companies.
Sony, Nintendo, Sega and many others have recently began to reintroduce older titles into the smartphone application markets. As a consumer, no one would want to pay for what is readily available on the market. Thankfully, developers like yongzh have posted his app for free.