Apple’s (News - Alert) iPad is still the best-selling tablet in the marketplace. In its fourth iteration, the tablet has a lot of fans and few complaints, though a few users have grumbled about the unit’s single output and lack of ability to use microSD cards to boost memory capacity. Complaints with earlier versions of the tablet centered around bleeding graphics and less-than-perfect microphones.

For Bill Gates (News - Alert), however, the iPad’s biggest drawback is its lack of real keyboard, and he recently noted that this lack is perhaps holding back growth of the Apple tablet.

"A lot of those [iPad] users are frustrated," Gates told CNBC. "They can't type, they can't create documents, they don't have Office there."

Gates, of course, was happy to point out that Microsoft’s (News - Alert) new Surface tablet is both a tablet and a portable computer, since it can “snap” into a keyboard and become the screen of table-top computer. Gates noted that the Surface RT and Surface Pro, Microsoft's two tablets, have keyboard options that make them more productive, according to InformationWeek’s Eric Zeman. The Surface Pro goes further, running a full version of Windows, including Microsoft Office, Outlook, and other features. The Surface, said Gates, offers the "portability of the tablet, but the richness of a PC."

It’s not surprising that he would shill for his own organization, but he may have a point. Web surfing, watching videos and playing Angry Birds is lots of fun, but what happens when you need to type a document or a long e-mail? Touch-screen keyboards work great for text messages or searching eBay (News - Alert), but for composing word documents? Not so much. For starters, they lack the same tactile quality that makes regular keyboards so workable. It’s too easy to “fat finger” the wrong keys and not realize you’re doing it.

In March of last year, iPad 3 reviewer Ardjuna Seghers   iPad shared these views on Trusted Reviews.

Seghers noted that, “Some tablet owners just want their device for couch-surfing and casual gaming. However, if you want to use your tablet as more of a laptop replacement, it’s an almost essential addition. The only ‘good sense’ reason we can think of for Apple not offering an attachable Bluetooth keyboard as an optional extra, is because this might impact MacBook Air sales.”

Of course, there are accessory keyboards available for iPads: LogiTech and Zagg both make portable iPad keyboards for under $100.