This is a surprisingly tricky question to answer. What is fairly unambiguous is that, for most people, increasing activity will correlate with better health. As a race, we are becoming more sedentary with longer periods of inactivity due to the large numbers of jobs that involve sitting at a desk combined with recreation such as web browsers and video games that similarly keeps us immobile. This study concluded that "intervention participants can realize modest changes in BMI and blood pressure with increases of physical activity". Now, the question is, are these step goals useful since, as you said, this could be taking time away from more effective activity.
In a study of pedometer tracking software with various forms of reminders, "participants found it beneficial to have secondary and primary weekly goals and to receive non-judgmental reminders." According to one summary I found, the reminders needed to be geared toward the participant's goals and did better when they provided specific goals such as getting 2000 more steps in rather than general "you should exercise more" reminders. On the other hand, other features, such as the provision of the number of calories burned, indicating "how much you can eat" have been correlated with weight gain. This is actually in agreement with general philosophies on exercise where it's been shown that people take the provided measures of calories burned as "free calories" and will consistently eat more than they burned as a method of rewarding themselves. So basically, the trackers seem to be providing benefits in terms of convincing people to be active more consistently throughout the day, but as with any form of exercise, you'll need to control your diet and not treat those calories burned as "free".
Lastly, as per my comment, yes, it's more efficient to do more intense exercise. Raising your heart-rate into a higher zone will improve your cardiovascular health. Doing resistance training will improve your strength. Doing activities at a higher intensity is more efficient because you're fitting the same amount of burned calories into a shorter amount of your time and you're challenging your body to get even better. That said, there's a reason why most people agree that exercising at least three times a week is a good idea but so few people do it. Most people are averse to extra pain and stress in their life, and face it, exercise programs generally involve pain and stress if done right. Yes, if you save five minutes of time by parking closer to work and you use those five minutes to exercise five minutes longer in a cardio or strength workout, it's going to be more effective in the end. But how many people will use those five minutes productively versus the number of people who'll use it to check their Facebook feed, to spend a bit more time at the water cooler, or to run one more check on their code? Providing feedback, and goals, for constant activity seems to just work in terms of getting those people more active, if not necessarily lighter.
So, in short, I think you're looking at two different axes. Counting steps is meant to promote an overall activity level through the day. Strength and cardio training is meant to promote more strength and endurance. Both contribute to your health, but in different ways.
