The information isn’t strictly correct, but the idea is basically right. The simple answer to your question is that the increase in size of the company implies an increase in size of the data requirements. The usual split is:

One- or two-person companies use Excel
The solution is simple and cheap and very low-maintenance. One person with knowledge of Excel can handle everything.
Very small companies use Access
This allows some data to be shared, although it’s not a very scalable solution. Again, it’s simple and it’s usually maintained by someone in the office who has a good grasp of MS Office.
Small-medium companies use Microsoft SQL server
Large companies use Oracle or DB2
This is a “real” database, but it lacks the enormous power of Oracle or DB2. The reality is that there is little to choose between these three in terms of functionality, but the MS solution only runs on Windows and doesn’t scale to the sizes needed by large companies.
Companies with extraordinary requirements for data use NoSQL solutions like Hadoop
This is Google and Facebook, etc.

SAP is not a database, but an enterprise software solution. It usually runs on Oracle or DB2 as its database. I have no idea why this was added to the list – it just doesn’t make sense.

Interestingly, DB2 is often forgotten by people when talking about databases, but it’s the second-biggest seller after Oracle – see Computer Weekly:

http://www.computerweekly.com/feature/Choosing-the-right-database-management-system