Maybe I'm missing something...
No, it's actually pretty simple...half of these people are truly obsessed with PPC that they forget (almost completely) about SEO and concentrate a little too much on their PPC efforts. What a waste... Yes, PPC is excellent! I'm a very hardcore fan of PPC but I also realize that SEO is long term when it comes to getting traffic to your site and referring sales.
I continue to get sales for several products that I no longer promote. Why is this? Because of SEO! I have links showing up all around the web that contain my affiliate link and people are STILL purchasing through these links. It's great! Especially when I no longer spend a penny or a minute of my time or money on making these sales.
So why would others be stuck on PPC? Are they afraid of a little hard work? Maybe... maybe not.
The truth is: PPC will get better Instant results. Yes, that's a fact. But when the cash runs out and the campaigns pause or end - then what? The sales end, too. So what if these people had been working on their SEO efforts and even Article Marketing on the side? They would have made a lot more money in the long run, that's for sure.
Search Engine Optimization is a major advantage for Affiliate Marketers, and I'm not sure why few speak about it. Maybe they try to keep it a secret? Maybe they view PPC as an easy way to keep the competition in and out, quickly and easily? Could be...
The fact is: SEO is just as important to real Affiliate Marketers as PPC. You can drive just as much traffic to your site with SEO than you could with your PPC campaigns, so make sure you are focusing on both.
While focusing on SEO - be sure to learn and understand Social Media Marketing (SMM) and take advantage of Web 2.0! Social Media sites such as DIGG, Reddit, StumbleUpon and others can bring you massive traffic in short amounts of time. Not to mention - these sites can give you extra results in the SERPS! YouTube? You betcha! YouTube can bring you a lot of traffic in many shapes and forms. Use it and use it wisely!
Do not stop with PPC... continue tweaking your site until you feel that you're going to get some great results for your keywords. Link from forum signatures, take advantage of other peoples blogs (please don't take advantage in a negative way, that's not what I'm referring to!) when you find an article to be of interest and use your site link (be sure that it's relevant!) so that you get extra trickles of traffic.
SEO is still a great way to bring in more profits with your Affiliate Marketing campaigns. Use it daily and do NOT forget about it!