I'm totally new in Salesforce but I'm here to go.
In this documentation page I read:
You can grant “Read” and “Create” permissions on all standard objects except products, price books, and ideas
Maybe I'm so still new to salesforce to be blind to such banality but.. Why? What products, price books and ideas has to be so special?
To answer the first part of your question, from the screen capture below, you'll see that products and price books are all children of Opportunity. Opportunity Line Items (OLI) are controlled by their parent because they're in a Master-Detail relationship with Opportunity. PricebookEntry is a child of Pricebook2 and is obviously related Product2. Because of this complex relationship, special permissions are required in order to create or edit products in Product2 and PricebookEntry. There's also one called ProductPick Admin
Ideas is related to Chatter and Chatter Answers. I don't know it's exact relationship to Chatter which I suspect could get rather complex as it can be enabled in communities as well as the main org (this is called zones). Its something an Admin has to enable and configure for an org. You can learn more about that by reading the Salesforce Ideas Implementation Guide. It appears that it has some Master-Detail relationships within it and would at a minimum have a complex child relationship with Chatter.
