Over the last week or so, I and millions of others have installed Windows 10. The upgrade happened seamlessly, and in an Apple-esque way, everything just works. Kudos to Microsoft for what has to count as the most ambitious software push in history.

Windows 10 not only offers consumers a more streamlined and useful experience. It’s also even better for software developers. That’s because unlike Apple and Google, Microsoft has given them one single platform to build for phones, tablets, PCs, and even the Xbox.

Developers stand to benefit in two important ways. First, this will reduce their costs. To build for any new device that supports Windows, a developer just needs to create for Windows 10. To build apps for Apple, on the other hand, a developer would need to create one in iOS for phone and tablets and another one in OS X for PCs. It helps that Microsoft is offering tools to make porting these apps even easier.

Second, it should increase revenues. That’s because with one platform for every form factor, developers will be able to target 1 billion users running Windows 10 by 2018. All those consumer will spend money in and on apps and will monetize for developers that support ads.

Lower costs. More revenue. What could go wrong?

Of course, there are ways this may not work. Chief among them is whether many developers who flocked to the mobile economy will see a business case for porting their mobile apps to laptops. For example, Instagram exists only as an app for phones and tablets. Does Instagram need to be on PCs? How about apps that work best because of their portability and location awareness, e.g. Uber?

More importantly, even if a developer wanted to build for PCs, why not just focus on the web browser, which has become the go-to platform for PC software over the last 20 years.

While I admit that I still root for Microsoft, my former employer, and am therefore not impartial, I do think that Microsoft can persuade mobile-first developers to build for Windows 10 and breathe new life into its moribund phone business. The key: what I’ll call the app-ification of the PC, or the notion that we use PCs to run apps.

PC app-ification requires two things to go right at about the same time for Microsoft. Consumers have to start thinking about apps on their PCs, as opposed to using the web, and developers have to respond to this consumer demand for apps by building more apps.

Both are primarily marketing challenges, and this is why I’m most concerned. Microsoft will rely heavily on its PC OEMs to tell the Windows 10 story. Here’s the first TV commercial I saw for a PC running Windows 10, in this case a Dell.

It does a lot of things right. It features a star born on the Internet, 19-year old Jenn McAllister. It shows how her Dell can work as a laptop or a tablet. She speaks to parents but relates to kids. Good casting call.

But at the 16 second mark, it becomes apparent that a 40-something copywriter is putting the words in Ms. McAllister’s mouth. That’s when she says, “Plus, Intel makes it super fast, even when I’m using, like, a ton of programs [my emphasis] at once.”

Programs? Really? I can’t remember the last time I spoke or even thought about a program. Reagan may have been in office. I bet Ms. McAllister never talks about programs.

If she’s anything like the rest of her peer group, though, she does talk about apps. The word “app” has become the catch-all term for software that runs on phones or tablets. If Microsoft wants consumers to demands apps on PCs, it has to call them by their proper name, and it has to do it often.

Microsoft has to recognize that neither consumers nor developers will change their behavior just because Windows 10 exists. They both need to be taught all about apps on PCs. If they do, developers will build those apps, and while they’re at it, they’ll publish them for phones, too. A Windows phone with every app available is a phone consumers will want to buy, and that would be the best possible development for Microsoft.