Short answer: no. You buy it from the Mac Store. This is printed pretty much everywhere on the web that talks about Lion.
Secondly: you're completely misremembering Snow Leopard if you think you downloaded it from Software Update. Apple never has and never will offer a full update for free. 10.x.1, 10.x.2, 10.x.3, yes, those are free. But the 10.x.0? Never. They come out on DVDs in pretty boxes and are released at massive events where nerds like us line up for hours to be the first ones in at midnight and grab a box.
Thirdly: yes but Apple reserves the right to limit how many computers you can put it on and not tell you until you hit that point and that's clearly stated on the App Store. Said same policy applies to all software and all developers; it's up to Apple whether they want to limit it to one computer per Apple ID, five computers, ten, or an unlimited number. I'm personally guessing it'll be limited to five at the most, but we won't know until it releases.