Microsoft is pretty much done with Windows 7, and now, so is Apple. The new 13-inch MacBook Air and MacBook Pro laptops introduced earlier in March will not run Windows 7 via Apple's dual-boot assistant, Boot Camp. According to Apple's support documentation, Boot Camp only supports Windows 8 and 8.1 on the new devices; however, official Windows 10 support will likely roll out later in 2015.
This is the second time Apple has decided to give Windows 7 the cold shoulder. The late 2013 Mac Pro also ceased to support Windows 7 in Boot Camp, but other Macs released in 2014 did support Microsoft's operating system.
The story behind the story: Apple hasn't officially said if the lack of Windows 7 support for Boot Camp is the new normal going forward, but it seems likely. In January, Microsoft ended mainstream support for Windows 7, meaning the OS will only receive security updates for the next five years, and retail disc sales for Windows 7 ended in late 2013. With Microsoft winding down its own support of Windows 7, now is the ideal time for Apple to say goodbye to it as well.
Not the end
Anyone who has Windows 7 discs kicking around will still be able to use the OS on the newer MacBooks—just not with Apple's software. Third-party virtualization options such as Parallels Desktop or VMWare Fusion still support Windows 7 installs. If you need a free option there's also VirtualBox, though Parallels or VMWare Fusion tend to offer better performance.
The lack of Windows 7 support with Boot Camp may annoy people who need it for work, but with the virtualization options around it shouldn't be a deal breaker.
If Windows 7 support is absolutely critical, however, and you want to use Boot Camp, there are still a number of Macs on the market that will support it. Check out Apple's support pages for a complete list.