Toyota is being more conservative.
In practice, with normal oil changes, because the DOHC valve train is
so short, and with four valves per cylinder, the valves are smaller and
lighter, plus generally drenched in oil (valve actuators under the cam
lobes) adjustement is generally not required.
Have known of people checking them regularly up to 300,000 miles and
still fine.

Toyota is being more conservative.
In practice, with normal oil changes, because the DOHC valve train is
so short, and with four valves per cylinder, the valves are smaller and
lighter, plus generally drenched in oil (valve actuators under the cam
lobes) adjustement is generally not required.
Have known of people checking them regularly up to 300,000 miles and
still fine.

These types of valve trains almost never need any adjustment unless parts
are wearing out. The -old- VW's that "needed adjustments" had a design flaw
with the parts in the head and are the only engine of this type I've ever
seen that had issues like that.

I've worked on Fiat engines that had pretty much the same configuration as
the one you describe.

Once initially set, they never needed readjustment, as others have
mentioned, unless you change
something like grinding valves, replacing valves, etc.

On one particular Fiat 128 that I worked on, the owner had just had a valve
job done at a dealership
in Houston.  The car was running pretty poorly, and I found the valves badly
burned.  The
'dealership' mechanic had ground the valves but had just reassembled it...
he never reset the clearances by using the disks, the valves went bad
immediately, and the
dealership wouldn't even respond to the owner.

I re-did the work, set the clearances (in one case had to grind a bit off
the end of the valvestem),
and put it back together.  The engine lasted until the car collapsed into a
pile of rust, considerably later.

So if you ever have to have valve work, be sure that the person who does it
knows what it is all about.