no it is actually easier to give dynamic IPs. For example, Time Warner my own an IP range of 64.0.0.1 ~ 64.255.255.254 or whatever. Then they set up their network, to assign that IP range to its clients. The IPs have lease times and will renew. Depending on server side configuration you can be assigned the same IP to your Modem's MAC address. So, their DHCP servers are broadcasting all the time, and once your modem is activated it knows that it can assign it an IP. Setting statics would be a lot harder, and they would have to be tracked in some sort of huge database so you never assign the same static twice.
Plus, when you micromanage your network you can set technology by IP. So, your ISP can say IP range 64.128.x.x is only static, and the rest is DHCP. That way anything that is IP driven can be assigned to allow x amount of bandwidth on this range, and y amount of bandwidth on this range. Then you can even set up things like VLAN.