The zero turns and the newer Kawasaki FJ180V's (for the Ariens 21") have oil filters, but the Honda and B&S single cylinder ones don't. The Honda engines in particular last forever for me, haven't had one quit on me yet.
The B&S motors I'm working to eliminate having any, as it might be made in america, but it's a crap brand. I needed a replacement motor for one of my zero-turns [thank you Kawasaki for installing the cooling fan incorrectly, causing the motor to overheat repeatedly], and went to Princess Auto to get the 24HP 2 cylinder vertical B&S motor, spent most of 2 days fitting the motor and rewelding the exhaust, turn it on, runs great, park it in the garage to go out the next day to use it, get in the garage in the morning, notice a couple spots of oil under it. Motor was dripping some oil. Fire it up again, and notice that when the motor is running, it's constantly dripping oil. Turn off the motor, drip stops. Great quality.
At least Princess Auto didn't give me a hassle about exchanging it for another one, which fortunately didn't have this problem.
Wish it had happened a month later, when PA got stock of some Kohler 22HP vert. motors which I would much rather have purchased, even if they are $500 more ($1700 vs $1200).