I guess I owe an explanation.

Most significantly, much of the Rails magic comes from Ruby. So when you say the two (WebForms and ASP.NET MVC) aren't alike, its like you are forgetting that they both use C#. The DLR is a small step, but it isn't in the same league. We can disagree that Ruby is such a significant productivity boost over C# - that's fine. But, if you think language is completely irrelevant, then imagine an MVC framework like ASP.NET MVC where you had to code your HttpModules, HttpHandlers, controllers, models and data access code in C. Concrete example? You don't do DI in a Rails app...yet it permeates through any WebForms/MVC app you write.

Then there's the tooling. WebForms and MVC share the same deployment and package management. Both are young and inferior to Cap and Gems (but they are young and they've done a good job with it so far). They are both hosted on IIS and essentially deployed/configured/managed the same. WebForms and MVC share the same IDE.

Then there's community. ASP.NET MVC and WebForms generally have access to the same libraries (nUnit, NHibernate, JSON.NET), the same resources, and the same community leaders (hey, I was one of them!)

So far, ASP.NET MVC and WebForms share: Language, Community, Tools, Libraries and deployment story. None of these are shared with Ruby.

Let's talk about code. Neither ASP.NET MVC nor WebForms have a cohesive model/data access story. Microsoft doesn't really provide an "M" with ASP.NET MVC. You can pick DataSets (oh wait, we don't like that anymore), or Linq2Sql (oh wait, we don't like that anymore), or Entity Framework (lolz) or NHibernate. Or, you can use Castle's ActiveRecord. None of these are very similar to Rail's ActiveRecord. So, when it comes to modeling and persisting your data, WebForms and MVC are exactly the same - which happens to be quite different than Rails.

WebForms and MVC share HttpHandlers and HttpModules/Global.asax. These are pretty nice (especially managed HttpHandlers in IIS 7). They also share the same built-in configuration management. But those are, yet again, something they share with each other, not with Rails.

Controllers? Ya, ASP.NET MVC shares more in common here with Rails than it does with WebForm's page model. And I agree this is pretty substantial..but even under the covers, things aren't all the similar. Email sending is very different (in Rails it builds on top of the controller core, which is why I include it here). Routing, model binding, validation...ASP.NET MVC and Rails are more similar than ASP.NET MVC and WebForms...but they still aren't that similar.

Views? ASP.NET MVC shares some stuff with Rails, but easily as much with WebForms. Asset management (or lack thereof), nested layouts...

Honestly, the only thing the two share in common is a controller with actions. And, when you look at typical ASP.NET MVC code, controllers/actions tend to do a lot more than than an equivalent Rails actions.

ASP.NET MVC shares more with Silverlight or WinForms development than it does with Rails.

EDIT:
Somehow in all that I forgot to mention that WinForms and MVC share the same framework (.NET) and runtime (DLR/CLR). Neither of which is anything like what Rails runs on.