I don't agree at all that even a true semi-auto manual (like BMW's SMG or Ferrari's F1) has no disadvantages vs. a regular manual tranny. Launches are more problematic (other than the launch-control mode on non-US M3s with SMG, which is so damaging to the clutch that it can only be used a handful of times with each clutch before it self-disables), there is ultimately less control than a car with a manual clutch, and the tranny is worlds more complex and prone to failure. Also, the BMW SMG seems to be the only one that does not enact a performance penalty (look, e.g., at the 0-60 times for an MR2 with sequential manual - it is something like 2 seconds slower than the stick). Also, true SMGs are very poor in full-auto mode, and provide a clunky, jarring drive when driven as automatics.
The bottom line is that I would rather drive a car with a stick than an automatic or semi-automatic even if it came at a performance cost (which it doesn't), because I find it a more fun, satisfying driving experience. To each his own.