How many SAME web2.0 property sites are effective as backlink source?

I know you can't just make 100 blogspot blogs and link to your site and expect to get the same backlink values as you would get from 100 different IPs/different web 2.0 properties. That's why you use different web 2.0 properties when you make link pyramid/link wheels for example, or use different class C IP sites as backlink sources.

However, a lot of people use web 2.0 properties and it is natural in a way you get many links "naturally" from the same web 2.0 property. For example probably the Apple's website have more than 10 (and probably many many more) backlinks from just wordpress.com or blogspot.com blogs.

So (in my opinion) it is not fair or natural if Google just gave value to one link from 1 web 2.0 property per site. Let's say if you are linked from 3 different blogspot blogs, then probably you would receive the same link value as you would get from 3 different web 2.0 properties(or websites with different class C IPs). Do you not agree?

But what about 5? what about 10?

There must be a cut-off point, otherwise as I mentioned in the beginning, you can just make as many blogspot blogs and links to your main site. But the cut-off point wouldn't be 1. (i.e. if you make 2 blogspot blogs and link to you site it should still be effective as links from 2 different sites).

Do you have any thoughts on this?