@Lord, from a layman's point of understanding, the DOLLAR is in high demand compared to the SHILLING.
Just to expound, the Central Bank of Kenya (CBK) is buying a lot of DOLLARS from the local market (NB: because of some pressure from some guys called IMF), therefore, making a deficit shooting the exchange price SKY HIGH.
EXAMPLE: When you buy East African Cables Limited Shares at KES14.70 in May 2011 and some other buggers want to sell theirs on 21st June 2011 at KES13.05, this is what they (the non-laymen/EXPERTS) call over-supply since everyone wants to buy them at KES15 and above.
From the above VERY PAINFUL example, the CBK is doing exactly the opposite, now that you (local Investor) are the LOSER, while Williamson, Kakuzi and Sasini being the GAINERS!
Hope you got confused, fellow layman!
Receive with simplicity everything that happens to you.” ― Rashi