|Cable modems come with only public IP addresses. I|
Wrong. What wanderer said above is correct:
With the shortage of ipv4 addresses some ISP's use their public ips for routing their lan traffic to the internet. They don't assign public ip to their clients. To accomplish this they give their clients private ip addresses.
Most, if not all ISP's use private IP addressing for their cable/xDSL clients. If you pay for a static IP (normally called a 'business class" package) you can get a public IP address. This is of course more expensive than a "consumer class" package which more often than not, gives you a private class IP address. The reason a company would want a public IP is so their IP never changes and they can run their own web server.
I guess they assume that you will only be connecting one computer in your home.
Wrong. They don't assume anything. When highspeed first became available the IPS's that offered it tried to make users pay for extra IP's for each PC/Laptop they wished to get on the internet so they could make more money. But once guys like me started showing folks how to use NAT software, they had to give up on that idea because they had no way of knowing how many PC's I was running from my NAT'd computer. Then of course hardware vendors started making SOHO routers which made the whole "multiple client PC's in your home accessing the internet through your one connection" a whole lot simpler and easier for even the least knowledgeable of users.
Cable is shared so the more PCs you connect in your house the more bandwidth you are sharing with others in your neighborhood and everyone's speed goes down
Well, you're half right in this statement. Take my house for example. Between my wife's work and home computers (She works from a home office) and my collection of computers we have over 10 PC's and 1 laptop connected to the internet. Since none of them are doing anything that eats up available bandwidth, we have no slow down issues.
However, if you, or someone in your home is up/downloading piles of large files on a regular basis (ie: software/videos/movies or music), then yes, that will slow everyone else on your LAN down because up/downloading large files really eats up bandwidth.
The DSL modems actually come with NAT because you have a direct connection to the ISP.
Wrong. A DSL modem only differs from a cable modem in regard to the type of media it connects to In the once case, a telephone line (DSL) and in the other, a coax cable (Cable). A modem is a modem is a modem. If you don't believe me, look up modem on the internet and you'll see I'm correct.
I think what you think you're talking about is a combination modem/router. A year or two back I upgraded my ADSL to a 5 Mbps package and with it came a new combo unit that is a modem/router/wireless access point. Because it has the router built in, it has NAT built in. A regular modem (ie: not a combo unit) doesn't come with, or do NAT.
"Bridging" is just allowing the data to pass through a device without having the device do much more than that.
Wrong again. Once more, I suggest you go use google and do some reading. Google "network bridge" and start by reading the wikipedia article. But don't stop there, there's a lot more info available.
I don't mean to pick on you, but misinformation is worse than NO information at all.