It is not equivalent to lies. But ommiting facts is a form of deception. Note the expression Do you testify that you will tell the
the whole truth,
and nothing but the truth?
These are three different elements of being truthful. Omitting truths violates the second category, whereas lying violates the first and/or third. So they are not the same. In some contexts, you are expected to be forthcoming, in others you can chose to answer the question as asked (and omit facts).
Culturally speaking, we seem to care much more about acts of commission than acts of omission. People seem to care more about an act of deceit, rather than omitting the disclosure of information. We believe that the only action you are responsible for is the act you take. I think this bias is worth reconsideration.
Personally, I measure the result not the method. If you lie to me, or if you neglect to tell me a relevant fact -- either way I'll see it as a deceit, and it will change my view of your trustworthiness. That said, getting the truth takes a well-worded question. This is an art form. In an adversarial context, the person asking the question needs to word the questions properly to elicit the whole truth, not just a truth.