Answer : Please make certain that you are comparing the same quality of jade. As with all gems, differing qualities creates different pricing. The majority of jade shops on the internet are selling treated jade such as Type B or Type C jade.
(See Classification of Jade)
If they cannot guarantee it is Type A Jade in writing, most likely they are not Type A Jade, no matter what they say.
If the seller can guarantee they are selling 100% real burmese jade in writing, they again are most likely not selling Type A Burmese Jade. Treated jade is still 100% real burmese jade. It is just not Type A Burmese jade. This classification(Type A , Type B, Type C) is an international classification and is used by the jade industry. Some sellers even produce certificates indicating the jade is 100% real burmese jade with 100% natural color. Again, read between the lines. Type B (See Classification of Jade) jade is treated to remove unwanted substances from its internal structure in order to make it more translucent. It is still 100% real burmese jade with 100% natural color. It is just not Type A Burmese jade.
Sometimes the color uniformity of Type B and C jades are too even. Again, that is not always the case.
Be sure to buy from a reliable source for Jade. Treated Jade is okay if you want one for purely ornamental purposes and structural integrity is not of primary concern. They deteriorate as time passes, so their resale value is quite low.
Answer : Imperial jade refers to Imperial Green jadeite found in Burma. Only jadeite with elements of Chromium (Cr++) are considered imperial green jade. They are a deep green in color and very valuable. A paler green is due to the presence of iron (Fe). Those pieces are not considered imperial green jade. They can still be quite valuable, although not as valuable as Imperial green Jade.