When adding new products you have to set Product In Websites attribute in Websites tab. Is there a way to set a default website automatically? I only have one website, so I think it is an unnecessary step to check the main website checkbox for every product. Am I wrong?
Did you try? If you only have one website you don't need - afaik - to add the product to the website. it is enough when you enable the product.
Not so easy way? Write a module, add a layout.xml file and change the template of the
tab_websites block in
app/design/adminhtml/default/default/layout/catalog.xml:261 and then copy the template and change it.
Easy and hacked way