Seems to work if you deploy a proxy on Google's app engine and use it to access WSJ ;)
A App Engine wouldn't have a IP with a reverse DNS *.googlebot.com, would it?
Nope, but it does resolve to something .google and if you check netblocks.google.com it will appear there so they might not be limiting it to googlebot only at this point.
Yes, but if one is interested whether an IP is from Googlebot or not, they would check if it resolves to .googlebot.com and not to .google.
I don't think that any server that random people can start a proxy on is in Google's SPF record.
not on the spf list, but on google's domain/ip blocks list.
The link you yourself posted says "The most effective means of finding the current range of Google IP addresses is to query Google's SPF record." While this is intended to be mailservers only, it has always appeared to me that the SPF list is all of their servers that 3rd parties can't run proxies on.
_netblocks.google.com includes only the servers that handle Gmail and corporate email.