the W1070 really is a short throw. It won't work for me at 20' on a 106" screen according to benq's site and projectorcentral.com
A short throw is anywhere between .1 and .7 times the screen width. If you can hit a 100" wide image from 70" or less then it is definitely short throw.
A typical throw range is about 1.2 to 1.5 times the screen width. So, a projector which can hit 100" diagonal from about 12' away is 'typical'.
Now, both projectors have a short zoom RANGE, that is, you don't get a lot of play with their zoom range. They are not 'super zoom' projectors like the Panasonic AR100 or the Epson 8350 which can go a great distance from the screen and still hit a smaller size.
This may be what is troubling you, but that does not make the 1070 a short throw projector. The W1070 can throw a 100" diagonal from 8'4" to 10'11", which is 'typical' for a projector.
In comparison, the Optoma HD33 can throw a 100" diagonal from 10'11" to 13'1" which is also 'typical' for this type of projector.
Now, in comparison, the BenQ W1080ST throws a 100" diagonal from 5' to 6' away from the screen. That's often perfect for someone who has to put a projector in front of a soffit, or a ceiling fan and still wants a larger image. In fact, it is the first home theater 1080p model which is remotely affordable which can do this.
Now, in all fairness, the W1070 is shorter throw than similar models such as the Mitubishi HC4000, Viewsonic Pro8200, or Acer H6500, but not much. Those projectors start at around 10' for a 100" diagonal, and go to 13 to 15' throw. But, not one of them can hit a 106" diagonal from 20' away. For that you need a super zoom projector, or a model with a long throw lens.
Edit: Just wanted to add, that while there are dozens of 1080p projectors under $2,000, there are only FOUR which can throw a 106" diagonal from 19' lens to screen (assuming 20' to your back wall, so, a foot less for the projector depth).
http://www.projectorcentral.com/projectors.cfm?g=1&hide=0&st=1&mfg=&p=500&p=2000&w=&r=13&br=&ll=<g=&t=&db=&dt=&c=&ar=&dvi=&wr=&pjl=&pjw=&pjh=&td=19&i=d&is=106&sort=pop&sz=15
Clearly 20' to 106" is a long way, and is outside the 'norm' for most projectors in that price range.
From 11 feet, 16 projectors can do 106" diagonal, including the W1070.