As per definition "Responsive web design (RWD) is an approach to web design that makes web pages render well on a variety of devices and window or screen sizes." [wikipedia] Thus, when you resize browser window it will rearrange the elements to fit the new size (which both your website and CTP do).
Could CTP do it better? Absolutely.
Should it? Not necessary, until the industry starts adopting responsive design more, which, I agree with you, it should.
But... there is a problem. Most people design their landing pages with Landing Page creators/editors which create non responsive pages to begin with, so there needs to be conscious effort on the part of the person creating the design to make it responsive.
Try surfing either CTP gauntlet or Leadsleap on a mobile phone it just is not comfortable doing it. In both cases, and this is also true for other TEs, because all responsiveness is left at the door of the surfing area.
Anyhu, I wouldn't hold my breath since it took the industry so long to adopt https, and that incompletely.
RE: What Is A Responsive Website? Take 2