I doubt about this, but still want to hear what others think. UPS condition power but does laptop's battery condition power?
An Uninterruptible Power Supply (UPS) conditions power by including electronics which removes ripple and noise superimposed on the mains AC supply.
It's main task is to provide power from an internal battery if the mains supply fails.
A laptop's battery is purely a DC supply with no ripple and noise, so while a battery doesn't condition the power, there is no noise and ripple to remove, so the effect is the same.
While there is some natural power conditioning when you go from AC to DC, a laptop's power supply does not really replace a UPS or power strip. That is not its function, nor is that built into it.
While you are going to get roughly the same DC whether plugged directly into the wall or a UPS/power strip, there is nothing in front to guarantee that the adapter will not be damaged, and allow damage to your computer if you are not plugged into the UPS/power strip.
There is a reason they sell laptop surge protectors.