HTC, Motorola, Sony, Alcatel, Huawei, LG and more all use Google Now on their Android phones.
Apple is taking this against Samsung because they are the only company they see as a threat to them.
Also, there’s the minor detail that Google Now and Siri have very little in common.
I’m saying this as a HTC and iPhone owner, and former S3 owner. I have no specific allegiance to any one brand.