BOSTON (MarketWatch) — What a showman Steve Jobs is. Last week the chief executive of Apple Inc.— emerging from sick leave — took to the stage to unveil his latest technological marvel, the new iPad 2. And in a bravura performance he successfully persuaded most of the world that it’s better and cheaper than its new competitor, the Xoom from Motorola. No wonder shares of Motorola Mobility Holdings /quotes/comstock/13*!mmi/quotes/nls/mmi (MMI 27.06, +0.11, +0.41%) have tumbled 10% since last week’s iPad moment, falling from $30 to $27. Apple’s stock, meanwhile, is up about $4 to $354 — near a record high....