Blog Valuations - where did they get those CPM's from?

24/7 Media has written an article valuing the 25 largest blogs, which are (summarised by Susan Mernit):

The Gawker Media: $150 million. 30 million monthly unique visitors.
MacRumors: $85 million. 544,000 visitors.
Huffington Post: $70 million. 4 million unique visitors per month.
PerezHilton: $48 million. 10.1 million uniques.
TechCrunch: $36 million. 3.2 million unique visitors and 14.6 million page views.
(tied): Ars Technica $15 million. Over 800,000 visitors.
(tied): Seeking Alpha $15 million. 400,000 visitors.
(tied): Drudge Report $10 million.1.1 million visitors.
(tied): Mashable $10 million. 5 million page views.
GigaOm: $8.4 million. 225,000 visitors.
Boing Boing: $8 million. 8.7 million page views.
Silicon Alley Insider: $5.4 million. 200,000 unique visitors.
ReadWriteWeb: $5 million. 300,000 visits but growing extremely fast.
Paidcontent.org: $3.5 million. 134,000 unique visitors and growing quickly.
(tied) Search Engine Land: $2.7 million. 225,000 unique visitors.
(tied) Smashing Magazine: $2.7 million. 325,000 visitors.
DListed: $2 million. 350,000 visits.
Daily Blog Tips: $1.8 million. 20,000 visitors.
(tied) Techdirt: $1.5 million. 400,000 unique visitors.
(tied): Neatorama: $1.5 million. 300,000 visits and growing very fast.
(tied): BuddyTV $1 million is too much about television. 800,000 visitors.
(tied):The Superficial $1 million. 522,000 visits last month, but dropping sharply.
Talking Points Memo: $860,000. 233,000 visitors and rising fast.

So far so good, but I was drawn to the assumed CPM's (ranging from $10 to $30 per page), which, as Susan also notes, are just a tad high:

I have some problems accepting these valuations when I know how much trouble many blogs have in getting decent advertising revenues--and how much run of network gets sold for a dollar or less in CPM, and even less in CPC.

Susan is too polite... I just don't believe them, based on my experiece of CPM rates over a number of web assets and blogs. Divide it all by 10 and you are probably closer to reality, after taking unsold inventory into account - and thats probably being generous.

Quite how the original writers came up with those numbers they don't say, but what is more interesting is how some ostensibly erstwhile blogs are picking it up and running it uncritically, which says to me that some of the commentators in this game are not that familiar with the basic economics

(By the way, GigaOm is valued at $8.4m on 1.4m pageviews/month - now we get a bit over 1/5th of that traffic (according to our logs, not Alexa I hasten to add), so if anyone wants to hand over c $1.6 m right now, we're all ears )