Well, no, this is still misleading. One specific portion of the service costs 10x more, not the whole service. Furthermore, its the one part of the service that Amazon doesn't really expect you to use (hence the price).
As you said, storage is not likely to be the most expensive part of your database anyway, so claiming "Google's BigTable Costs 10 Times Less than Amazon's SimpleDB" is misleading at best.
Well, no, it's still accurate. Amazon's SimpleDB is a separate service. If you are trying to store a very large number of relatively small objects, like sessions or digg-like data, the S3 pricing doesn't come into it. Once again, it's not a claim that Google's datastore is a tenth the price of Amazon's SimpleDB. It's simple observation. If you want to say "Using Amazon data services is as cheap or cheaper than Google AppEngine" or add other services to the comparison, that's your prerogative. But the comparison of pricing for two services is not a claim and it's certainly not "ridiculous."
Claim: "Google's BigTable Costs 10 Times Less than Amazon's SimpleDB".
Fact: Structured data storage on BigTable costs 10 times less than structured data storage in SimpleDB.
Those two statements are not the same. Implying they are is very disingenuous.
"But the comparison of pricing for two services is not a claim"
Using one of four different factors (completely ignoring S3, which in and of itself isn't exactly fair) to compare pricing is making a claim that isn't supported by the evidence. If you provided a typical actual breakdown of storage costs versus access costs, and then used the total differences in price structure to arrive at a comparison price, then could make a claim about the comparison between the pricing for both services that was actually based on facts.
As you said, storage is not likely to be the most expensive part of your database anyway, so claiming "Google's BigTable Costs 10 Times Less than Amazon's SimpleDB" is misleading at best.