A DDoS attack is quite different then DoS attack though, and really is a different ballpark, both technologically and in terms of the sophistication needed to launch an attack. In other words, a echo request attack is script kiddie 101, a true flood takes a bit more effort (unless I missed a botnet firesale online)
My 10/1 cable modem can easily use this type of attack to take down a user on a 2Mb/256Kb level of service with a pure DoS -- In other words, this type of attack means all I need is for my upstream to exceed the victim's upstream, rather then a traditional flood which would require my upstream to exceed the victim's downstream.
If I don't care about spoofing my IP, I could do it from the Windows command prompt by launching the right number of ping.exe sessions with some carefully tuned packet sizes.
"Decent firewalls" != "The cheapest NAT box at Best Buy" (in other words, I don't believe most people have a "decent firewall")
Let me also say that I personally believe anyone advocating disabling ICMP is flat out ignorant and unqualified to dispense advice, and anyone advocating discarding echo requests in the name of security probably has a similar misunderstanding.
As someone with more then a passing interest in both security and DoS/DDoS prevention/survival, I consider it important to understand the risks.