Sorry, I should have answered more in depth. I take the existing size and layout of the swf and just stretch it to match whatever screen space is available, regardless of size / aspect ratio. This tends to work well for the majority of games, and buttons are still touchable and everything is readable.
No new artwork is needed.
Google Play does require an icon 72×72, a high res icon 512×512, 2 screenshots 800×480, and a feature graphic 1024×500. If a designer wished to make new artwork for that then that would be fine but most commonly I use the existing artwork for it.