@jlocke, yes you're right that Google has pant loads of money. The primary reason for this change IMHO is to extend its reach yet further onto other websites (all those using alternative analytics solutions and who have so far resisted surrendering your page view data to the power of G).
The SSL implementation cost in absolute terms is clearly significant, but perhaps not in relative terms too. Google is very efficient at data center management and we can conclude that its search servers are pretty much near capacity. Google reportedly has in excess of 1.5 million "servers". This probably includes a variety of device classes (network devices such as load balancers etc).
Let's group it all together as a big compute hardware cloud. SERPs are G's core business (without that it would have only a tiny fraction of its current power) but clearly only a fraction of those servers are dedicated to real time SERPs generation (the rest are doing maps, search indexing, crawling, hosted apps etc), but let's say it's 10% for the sake of argument. That's approx 150k nodes.
Now if Google rolled out SSL across all search globally, even if the Google system architects optimize the cost of adding SSL acceleration to say a modest 10% increase in compute resource, you're looking at adding 15k new nodes.
I guess the cost could only be in the low tens of millions then.
Not loose change for most companies, but as you say not majorly significant for the king of text ads.
I think Google's ambition is not to organize all the world's information, but more accurately, to capture everything every individual does on the web.