The claws are out over the absence of Live View in the Alpha 700. Personally, it would have been a nice feature which may have the occasional use but not a terribly important ability in a DSLR as it is currently implemented. There are several plausible reasons why Sony decided not to follow the herd.
Marginal Utility: Without a swivel screen, the shooting position is still confined to an arc directly behind the camera. Possibly to reduce sensor heating, the frame rate on the D300 is only 15Hz which is quite jerky. The 40D supposedly has a refresh rate of 30Hz but the screen is only 320x240. The 40D does not have contrast detection AF but relies on flipping down the mirror to take AF readings. The D300 does have contrast detect AF but Nikon say it's only really for tripod work. All of these concerns can be addressed as the system is developed but as it stands, Live View has serious drawbacks in its operation.
Added Cost and Mass: Implementing Live View is not simply a matter of reading out the information from the sensor in realtime. The mirror has to be flipped up and the shutter left open for extended periods of time, similar to bulb mode. This will increase power consumption and may require new mechanisms to deal with the different operating mode. To make Live View useful, Canon have used two separate motors to flip the mirror and cock the shutter independently allowing the shutter to operate without the mirror flipping. This means added mechanical complexity, weight and cost, engineering effort which could be applied elsewhere instead. To make Live View really worthwhile, an articulated LCD is required which also would increase complexity, weight and cost.
Integration: Sony will not want to implement a feature without it being polished enough to match the rest of the camera. Live View, in the opinion of Sony it has been reported, currently is not in the proper state for prime time integration with DSLRs, though I'm sure they are working hard at making it work to the best of its potential.
Thus the question of having or not having Live View does not have such a clear cut answer. There are many engineering issues as well as the all important marketing angle and it seems Sony, for the present, has allowed engineering principles to take precedence.