Graphic designers, perhaps. Movie studio's, no way. They need the ability for better multi-display support, graphics cards, internal SATA drives, and more cores. This is especially true for HD content rendering. An iMac is still limiting in upgradeability, while a Mac Pro can last longer with incremental updates. Pricing, a top line, loaded iMac (what you would need to compete with a Xeon Westmere Pro) will run you ~$3k before taxes, placing it in the same price range as a decent Mac Pro and you will get more for your money with the Pro (and many professional prefer to use their own displays, EIZO being the preferred display with a hood as anti-glare displays simply diffuse/pixelate images).
In short, the Mac Pro is still the number one choice for professionals who need the power for the price, upgradability, and use of their preferred displays.