Buck converter without inductor in a NiMH charger (Zilog AN0259 application note)
The circuit you mentioned could be described as a pwm current source. It uses its relatively large 2 ohms current sensing resistor, as well as the resistor R3 at the base of Q1 to limit its output current.
A quick simulation shows that there is significant power dissipation in the other Q1 (BD140) during the on phase of the pwm cycle. So to answer your question: It looks like the designers just &quot;rolled with it&quot;.

If you consider using this circuit i would like to advise against it since it relies solely on software intervention in case of overcurrent. Also, there is no fuse.