When future historians look back and try to determine the exact moment when the personal computer and desktop form factor started to decline, there will be a lot of pointing at Jan. 27, 2010 – the day Steve Jobs announced the iPad. In truth, the downward spiral isn’t marked by one event, but a lot of little incidents that mark the trail.

On March 13, Adobe unexpectedly added a chapter to the story of the fading of the PC, when it announced that it would be closing down its BrowserLab service effective… March 13.

The closure was as surprising as it was abrupt. BrowserLab enabled developers and web designers to test their work on different desktop browsers and operating systems, to help ensure cross-platform uniformity in look and operation.

In a statement to users on the BrowserLab blog, Bruce Bowman, Sr. Product Manager Edge Tools & Services and the Adobe BrowserLab Team, cited the popularity of mobile platforms as the big reason for BrowserLab’s deactivation.

“When we originally launched BrowserLab as a free service back in 2009, our customers were struggling with testing their web content across desktop browsers and platforms. Since then with the growth of the importance of mobile devices and tablets, the landscape has changed dramatically. Because of this shift, we have seen the usage of BrowserLab drop over the past year while at the same time our engineering team has been focusing on solving this new challenge with new solutions.

“Due to this, we will be shutting down the Adobe BrowserLab Service effective immediately,” Bowman added.

The resources BrowserLab must have taken up for Adobe must have been significant, for them to want to retask their team to focus on mobile development. Adobe has long been a strong presence in web design, desktop or otherwise, so it seems odd for them to abruptly drop even an ancillary service like this. While no one would argue that desktop is in decline, it’s not completely going to go away.

An unspoken reason here may also be the way major browsers use rolling release schemes, where updates happen transparently and rapidly. Keeping up with those many different browser releases may have been too much of a challenge for Adobe, especially if is focused on delivering a similar service for mobile developers with its Edge Inspect product.

BrowserLabs users won’t be left in too much of a lurch: Bowman specifically pointed out BrowserStack and Sauce Labs as two viable alternatives to BrowserLab.

In the grand scheme of desktop these days, I suspect the departure of BrowserLabs will create little more than a ripple within the development community. But it is one more signpost on the shift from desktop to mobile, and a potential harbinger to developers focused on the desktop that their tools and services may one day disappear.