I don't even see how the Sportster fits in that comparison, other then the retro looks and low technology, which I definitely see as good. But aside from that, the Sportster is a much smaller bike. I just don't fit on it. I haven't tried the Guzzi, but I have sat on the Bonnie, and it has a LOT more room than the Sportster. I really like the Sportster, just wish it was bigger.
As for the Bolt, it is basically a Japanese copy of a Sportster, and seems to be just as small. A big part of what attracts me to the 3 bikes in the test is that none of them were Japanese. None of them are copies, they are all original, and they all have a heritage. They are not exactly the same as their half a century old ancestors, but they are remarkably close considering some of the high tech junk out there today.
2002 Vulcan 750, 2001 XT225
2008 Vino 125, 2009 Genuine Stella
2012 Zuma 125, 1980 Puch Newport moped