As per discussed in the MTW threads horses would charge a wall of spikes, its the Humans that might not want to.

You can still play defensively. It just depends what you're coming up against.
And yes receiving a charge doesnt work as well in RTW as MTW, but on the other hand countercharging puts all sorts of holes in your line.
This is why I always deploy with two lines when fighting defensively. One line up front (Triarii or Infantry depending on what im facing) to "counter charge" and one line behind to plug the holes. If your "countercharge" troops are getting isolated and picked off you can always send in your second line or have the opportunity to use some flanking manouvers. Because I dont seem to have the 20 second fight problem most people have, this works well.

Also I always use guard mode on ALL my infantry even when on the offensive, which might have something to do with it. Chasing down routers is not infantries job, skirmishers/cavalry/wardogs yes.