The bottom two examples are enough to show that the signatures on the letters are not identical. Note the loop at the top of the "O" by the downstroke on the signature on the left; that loop is absent on the signature on the right. The other signatures are difficult to make out due to the low resolution, but I believe it is possible to detect small variations there as well.
The other reason I question the electric pen claim is that there is a well-known specimen of the president's electric pen signature. In May 2011, the president was in France when an extension of the Patriot Act was passed by Congress. As was widely reported at the time, and to some minor controversy, the legislation was signed into law by President Obama's authorization of the use of an electric pen. CBS News reported this at the time, and had obtained a copy of the legislation with the president's electric pen signature:
The differences in the "B" alone are sufficient to show they are not the same.
However, missing in all this is whether or not the machine the White House uses for electric pen signatures is programmable to add variations to give the appearance of uniqueness. The International Autopen Company refers to "signature templates" in their description of one of their products, so obviously it is possible to have more than one version of someone's signature available for use. Comparing the signatures on all 30 military families' letters might shed some light since it seems unlikely the White House would store that many versions of the president's signature, so presumably some duplication would show up. This, however, strikes me as overly conspiratorial and not worth the effort.
The remaining issue, of course, is the use of form letters. Although not unprecedented, as noted by Jake Tapper, President George W. Bush generally eschewed their use when writing to grieving families and choose to write personal notes to the families. Given that President Obama's letters are dated September 23, 2011, and he spent the following afternoon on the golf course with Bill Clinton and White House Chief of Staff Bill Daley, it would be difficult for the president to plead lack of time as an excuse for the fill-in-the-blank condolence letters.
Thanks to Ed Morrissey at HotAir who linked to this post as his Obamateurism of the Day.