IBM, the industry giant is also ready to give its UDB DB2 for free. Last year Microsoft offered, SQL server 2005 Express Edition  without any charge. Also, Oracle in the same time offered its 10g Express Edition for free.

Database giants set their basic version for free, which is mainly due to the free & open source databases like MySql, Postgre SQL etc.,  Basically I work in Microsoft Technologies/Products, but for certain things I still use MySql. Also many hosting companies provide Windows hosting with free MySql database. Even Sun lets its source out & making Solaris 10 free to download. 

So, now a days people are more interested in going for free packages rather closed source / paid softwares. In 2003, when I was working in Indian Red Cross Society, New Delhi, I used to meet many people across the globe & who are from non-IT field talking about free softwares. And now many people here in India prefer free / open source products. In general, students are very much interested in open source softwares, so these are the main reasons for the giants to let their basic versions for free.