I don't have any experience with CMTS or DSLAM but I do with LAN and WAN switching and routing. I would guess that it is much easier to "throttle" a connection on the Provider/DCE side of the connection than it is on the Customer/CPE/DTE side - simply not having to transfer config files and such. Also, by controlling it on the provider side, it wouldn't be as suceptible to "hacking" as article 2 illustrates.How to Un-Cap a Cable or DSL Modem
"Cap" is a reference to an artificial limit on downstream and/or upstream speeds. Such caps are common on consumer-grade service. "Un-capping" is thus an attempt to remove such limits (and thereby increase speed).
However, un-capping is an urban legend (or hoax, take your pick) -- subscribers cannot un-cap cable or DSL modems:
Cable Modem speeds are controlled by the CMTS (head-end box for Cable Internet)
DSL speeds are controlled by the DSLAM (head-end box for DSL)
(Note that if you did somehow find a way to do it, that might be construed as theft of service, with unpleasant consequences.)