device sio vs. device uart

Originally I posted this to questions_at_ but got no answer so I'd like to ask 
here:

Hello,

after compiling a custom kernel with device uart instead of device sio I 
see the following in my boot message:
sio0 failed to probe at port 0x3f8 irq 4 on isa0
sio1 failed to probe at port 0x2f8 irq 3 on isa0
sio2: not probed (disabled)
sio3: not probed (disabled)

But I don't have sio in my kernel at all.

Can someone please explain me the major differences (besides the newbus 
adaption) between sio and uart? And why is sio still in GENERIC?
And of course why do I see these sio messages?

Thanks in advance,

-Harry