Was doing some general testing and found out that for a managed solution, the custom views still can be deleted. The ability to delete is same even when the custom view is set Customizable=False.
I think this is wrong and should be fixed.
Even though a view can be rebuilt anytime and has no data impact upon delete, there may be situation where solution provider wanted a managed (custom) view to be prevented from deletion.
For example the Customer Portal accelerator uses the specific View name to list grid columns:
Under ViewCases.aspx.cs, line 48, CaseList.ColumnsGenerator = new CrmSavedQueryColumnsGenerator("Cases Web View");