most of the biggie tech companies like Microsoft focus mainly on data structures. It appears as if data structures is the only thing that they expect from a graduate.
No, there's more. For example, we also expect that you be a quick learner who can learn new frameworks, APIs or even programming languages within a short amount of time. That's a bare minimum bar. Someone who takes a long time to learn a new framework, API or language will not be a successful developer on most teams at Microsoft.
And of course there are many more aspects that we focus on in interviews other than just raw knowledge of data structures. Ability to deal with ambiguous specifications, for example, or ability to recognize coding patterns that produce insecure code, or a dozen other things. But ability to understand data structures certainly is a very big one.
It is particularly the case that interviews are biased towards testing knowledge of data structures for recent CS graduates. Recent graduates, most of whom do not have a lot of real-world experience, are not expected to be good at the same sorts of things that someone with fifteen years of industry experience would be good at.
I must confess that I was not so strong in data structures
It's good that you know that about yourself. If you're unable or unwilling to change that about yourself then my recommendation is that you don't apply for a job that requires facility with data structures.
there is this general perspective that a good programmer is necessarily a one with good knowledge about data structures.
It's tautological that a good programmer is a programmer who is good at building the sorts of programs that need to be built. Lots of programmers work on tasks that do not require deep knowledge of data structures. Some of them work on tasks that require a deep knowledge of user interface design, for example. Or database normalization. Or whatever. Those people can still be "good programmers" in their domains.
why all this emphasis on Data Structures?
I ask interview questions about data structures because on my team the developers design, implement and manipulate complex data structures all day every day. Yesterday we had four hours of meetings in which a half-dozen developers argued the pros and cons of adding single Boolean field to a particular tree node. There is probably no skill on my team more important than ability to understand data structures at a deep level. It would be foolish to not ask interview questions about it, since that's what we do.
Does not having knowledge in Data Structures really affect one's career in programming?
Well it certainly will prevent you from getting a job on my team. But like I said before, programming is a huge field. There are lots of kinds of computer programming that don't require knowledge of data structures.
is the knowledge in this subject really a sufficient basis to differentiate a good and a bad programmer?
No. But it is almost always sufficient to detect developers who are unlikely to be successful at Microsoft. Since that is what I am primarily interested in detecting, knowledge of data structures is one of the factors I test for in interviews.