Hopefully they rent a core aerator as apposed to a spike aerator as a spike aerator compacts the soil. Additionaly since you know what thatch is and you think you have to much you probably do but your new lawn care folks are trying to save the cost of that rental. Just keep in mind that dethatching and core aeration may make the lawn appear a bit roughed up for a short while but it will bounce back better then ever.
On the subject of lawn care and since its time to fertilize be carefull what fertilizer you use. Many have too much nitrogen in them. While the high nitrogen makes the grass turn green too much promotes thatch, insects, etc.
http://aggie-horticulture.tamu.edu/e.../lawnfert.html