Why PCTINCREASE defaults to 50? IMHO the only reason are lazy/unknowledged DBAs and developers.
Supose the tablespace default INITIAL parameter is 10K and default PCTINCREASE would be 0. When a new table (or index) is created without specifying storage, when the table grows to 100M (a rather tiny table nowadays) it will be consisted of 10,000 extents! This bares huge consequences regarding the maintaining of database dictionary and (in such an extreme case) also on performance when scaning such a table. If you apply PCTINCREASE=50, you will get 100M table in only about 20 extents. If I would have to choose between a table of 10.000 equaly sized extents and a same table of 20 differently sized extents I would choose the second option!

However I agree that PCTINCREASE should alway be 0, but also INITIAL=NEXT size should be set correctly at the same time.