Yes in part that is very true. The other part is that link ads are generally worthless, I'm talking from experience... If you add link ads to your site the number of clicks will increase but earnings won't be that amazing.
I like link units because it looks good on my site. The CTR is also okay but my MAIN problem is the I always get a penny or two per click.
Just for the link ad sceptic's confirmation, I have a website with one adsense ad and one horizontal link ad per page. I make well over $10 per weekday on this site with only 5XX unique visitors. 48% of the clicks are on the link ad and 52% on the adsense ad (which incidentally is the large rectangle). Virtually the same stats apply to the income, that is 48% of the income of that site comes from the horizontal link ad and 52% comes from the adsense block. In short form, ignoring the link ad (thinking that two clicks to make money is not worth it) is a bad idea, I have virtually doubled my income after successully blending the link ad into the design of my site. The link ad is blended to look like a menu, even though the fonts are different to my menu system. I have not yet incorporated the search function and do not plan to do so.
And I could publish statistics that validate the skeptic's position. As I and others have said, your mileage may vary. They seem to work well for your site, though. Mine, not so well. JimBob's site is somewhere in between. It's like all things Adsense...everyone is going to experience something a little bit different. If they work, use them. If they don't, you can still leave them there if they don't uglify your site because every bit extra they make is something you wouldn't have without them.
I put links ads right under the navigator bar and it's works good. even better than ads block somehow.
I would always prefer the Ad units (specifically the Text ads) as they pay out more than any other type of unit. Link ads may work for you depending on your site content and traffic.