why don't most classes extend PEAR?

hi everyone, i'm exploring pear; have used DB class in the past. question: in spite of PEAR as a recommended base class, i've noticed that most of the classes in pear directory don't extend PEAR. is there a good reason for this? is it perhaps so that classes can not be tied to dependence on pear php installation? i notice that PEAR.php calls dl(PEAR.so); i guess this might be a problem if your code is hosted somewhere that doesn't have PEAR.so installed. related question: if i write a class that extends PEAR, shouldn't it be called PEAR_myClass and reside inside pear/PEAR directory instead of inside pear? I thought this was the intended convention on directory structure but the cvs tree doesn't reflect that. sorry if these questions have been answered already but i didn't find them faq or anywhere. thanks, greg