Sure, they let some through - but not enough to support the people there on anything more than a borderline subsistence level.
http://www.ipsnews.net/2010/07/mideast-israel-chokes-gaza-de...
http://www.ipsnews.net/2010/07/mideast-israel-chokes-gaza-de...
Israel provides the residents of the Strip with food, water, electricity, medical supplies, etc. The residents respond with rockets aimed at Israeli civilians.