To illustrate to project stakeholders and help them appreciate the difference between a typical PaaS scenario and IaaS scenario, I have drawn these two diagrams:

PaaS - typical scenario

  IaaS - typical scenario

The intent was to show how the PaaS hosting must make a commitment by recoding to the platform Azure, while IaaS is portable.

Can you let me know if you find anything off or not right? I am relatively new to Azure and something here may be incorrect.

thanks in advance.

You got it right on your own :)

Key difference would be what you have under control (and price).

PaaS model you have very little influence over settings. You can change few things but if you may have to change code to adjust to invironment.

In IaaS model you have control over everything from OS level and up. You can change almost everything so you can change environment to setting you want (or have now) for your app.

Hi,

 The illustrations are pretty good, They definitely outline the Portability advantage of IAAS over PAAS, mainly because of runtime difference between PAAS and On-Prem setup, you will be needing to recode your application in-terms of diagnostics, multi-tenancy and storage access.
 FYI, also refer the below excellent article on the differences between IAAS and PAAS.
 http://blogs.msdn.com/b/hanuk/archive/2013/12/03/which-windows-azure-cloud-architecture-paas-or-iaas.aspx
 
 I would also suggest you take a look at the Azure App Service - Web Apps if you haven't yet, It is another Excellent Service which is a fully Managed Platform for professional developers that brings a rich set of capabilities to web, mobile and integration scenarios. Quickly create and deploy mission critical web apps that scale with your business.
 https://azure.microsoft.com/en-us/documentation/articles/app-service-web-overview/
 
Regards,
Nithin Rathnakar

• Edited by Nithin.RathnakarMicrosoft contingent staff, Moderator 13 hours 39 minutes ago edit

Thank you.

Can you comment on the "Cloud Service" vs "App Service" containers in the PaaS diagram (middle tier in the first diagram)?

In a typical Web app or Sharepoint scenario, which makes more sense?
App Service, Cloud Service or Web App?

Nithin is right. Web App is exellent way to go. It very easy to manage and has fantastic agility.

It's hard to tell what is best  in your case. You need to evaluate pros and cons for every option and decide what is best for your app.