When ever the product company gathers some new information from the market place from some potential customers, they try to include it in their product and hence the requirement changes frequently. 

In projects based applications, as one client only gives the requirements there are not many changes in requirements and hence testing also becomes less tedious than product testing.

 In product based company, the tester will come out with creative idea about the products. He should think like a client/end user when changes were being made. products are basically should have less work and more out put to client.

 Where as for applications , once it is done it will be implemented and maintenance work will be there once in a year as per the company policy