To keep it simple. Every time you pass a packet it must ping off the Dns address server, get your current ip, then transfer to your ip.
If the dns address server fails to deliver your ip address, your ip server will recommit the packet and try again. With a static is a to b. With dns server it is a to b to c. If packets into b exceeds the bandwidth of the dns server, your connection to c will slow. Regardless of what the connection of a and c are, you need to wait for b to pass packets.
In simple terms, you have 3 guys with radios. Person 1 and 2 do not change channels. Person 3 must change channels every few mins.
Person 1 call person 2 to get the channel for person 3. If person 2 does not answer back, person 3 can not be contacted. With wimax it is alot harder.
Because you have like 20 people, and 10 of them are changing channels. But with wimax, they system knows when 1 of the 10 stop communicating, and just works around him.
Bottom line is that if your dns server stops tell you the new ip, your connection will slow or stop. It just adds another step in the process.