It isn't the corporate size that is the issue, it is the size of the patent portfolio that IBM has. I would not doubt IBM's response to any of your scenarios is to find 10 or so patents key to Oracle's database software and file a patent infringement case.
I don't think we are underestimating Oracle, we are just given IBM their due.
>>> "a gerbil attacking a tiger"
> It isn't the corporate size that is the issue
And note I originally gave IBM as an example of just ONE possible target after Google. So you selectively challenge one point and then even on that point dismiss the other issues (like the "low blow" argument where Oracle doesn't even have to sue the target, be it IBM or some other deep pocketed corporation.)
I admit to a bit of confusion on your response. I was pointing out in the "low blow" scenario that Oracle is much more vulnerable than IBM to a contest of patents. Oracle might not be suing in your scenarios, but that wouldn't stop a suit by IBM.
The crux of this whole thing is that Google isn't using the GPLed version, wasn't paying a license fee to Sun, and isn't to Oracle. Oracle believes Google should and (probably after failed talks) is filing a lawsuit. IBM and Blackberry payed to license like other companies. So, Oracle really has no reason to sue anyone but Google.
AFAIK, Oracle can pull a low blow like not licensing Java to IBM next time or perhaps more subtle putting ridiculous clauses for new standardized versions. They can even do so with popular support by switching to Affero GPLv3, for example. IBM would never run something like that license due to the patent-related characteristics of it.
I wouldn't underestimate Oracle.