The are all split-second chameleon,
and most of those are such that

posting changes on their site is enough by the owner,
rather than requiring anything more like notice
and
accessing the site to see if there were changes, would
constitute agreement to them if there indeed were changes

.



The split-second chameleon issue is


at time    T minus 0.2 seconds  ,
person checks and there were no changes

at time T, person starts using the site

at time    T plus 0.1 seconds  ,
the owner posts changes

it takes until    T plus 0.2 seconds
for the person to stop using the site


resulting in the person being bound
by what the terms were changed to.



The github terms are least-bad in this latter respect, but


"such as price increases" is the closest
those come to defining "material"ness

and

Posting changes on their site is enough by the owner.
One might try arguing that 
accessing the site to see if there were changes
is not "use of the Website", but that seems to me
like it would be a very difficult argument, because
the previous sentence instead says "use of the Service"
and the Definitions section specifies that 
"Website" refers to    ", and all content, ...
provided by Github at or through the Website."


.