It sounds like the USB drive doesn't have the drivers to boot the other macs. :-(
The fastest path forward is to simply erase install a basic Snow Leopard OS onto the failed macs. While this is happening, do download the 10.6.8 Combo update to your USB drive just in case it's needed.
Don't bother running the updates unless the Lion installer forces you to get to a higher version than your 10.6 installer delivered.
Once you boot into Snow Leopard - you can try again to mount the USB and execute the Lion upgrade package. I don't know if it runs well from the USB or needs to be copied to the internal boot drive.
There's a little uncertainty in my brain - so I don't want to write too much without making sure this makes sense to you.
As an alternative - you could try instead to transfer the recovery partition, but this may not be universal (include the drivers the older macs) either.
There is a step-by-step recipe here for copying any bootable volume to one file on a USB drive.
If you are curious or feel it's worth a shot, image the recovery partition from your Lion mac.
You should be able to boot from DVD and use disk utility to make an equivalent partition on the "non bootable" mac and drop the recovery data to get a minimal bootable system and avoid a full Snow Leopard install.
Unless you are familiar with Disk Utility and the steps to capture, the reinstall option might be more likely to succeed on first attempt. I certainly don't know if this partition is customized by Lion and not universal so I've made it an aside for the curious.
Any time you have problems starting a mac with an installer - do check these three articles:
In your case - you probably have a MacBook Pro (Early 2011) which will boot from (Mac OS X v10.6.6 Build 10J567) or later. You might see the term "retail disk" which means it has drivers for all Macs that can run that level of OS - this is different from the disks that ship with macs - you almost never can use say a MacBook Air restore disk on a MacBook Pro - they just have the drivers for that one model.
Normally, you could just buy a retail copy but the last 10.6 retail copy I've seen documented is 10.6.3 and is too old. You'll need to order a replacement disk through AppleCare online or via phone (or find someone in possession of your MacBook Pro's install media for Snow Leopard)
Most Apple Retail stores are set up to image your mac from the factory builds through the genius bar and since your mac is so new, I can't imagine the seller you bought it wouldn't bend over backwards to make sure you got a copy of the appropriate disk (they might even have a service desk that could assist you)
Best Answer
I'm not sure if this will work in your case. But I have a 2010 MacBook Pro I cannot install the retail copy of Snow Leopard onto. That retail disc is 10.6.3, and the laptop needs a higher version.
To overcome this, I installed Snow Leopard on an external drive connected to an older Mac. I then updated Snow Leopard to 10.6.8 and copied the contents of that drive back to my MacBook Pro via SuperDuper.
Now, in your case, I'm not sure if Snow Leopard will work at all on the recent MacBook Pro. But, if you have access to an older Mac, give my solution a try.