The BMW i3 concept car at the 2012 Detroit Auto Show in January. (John T. Greilick / Detroit News)BMW will sell cars over the Web for the first time as the world's largest maker of luxury vehicles seeks an inexpensive way to reach more buyers to recoup spending on its electric models.A direct online sales platform for BMW's new I sub-brand will be unique in an industry where, outside of small-scale experiments, competitors leave Internet orders for cars to dealers. BMW's range of strategies for the models, including a roaming sales force backing a limited showroom network, reflects the challenge carmakers face as low-emission vehicles trickle...