I have a similar grade progression as you do, and honestly, I think it's almost saying more about you that you have gotten to the point where you can achieve solid A's for your last two years (I'm assuming that you have done this, of course, based on your treatment of your B/C semesters). It shows that you are able to grow and produce great work in more advanced courses. Grade-hungry students generally aren't good PhD material, as far as I can see. It's all about passion, hard work, and a desire to grow as an intellectual. A perfect undergrad GPA only reflects strength in background material.