some manufacturer sees a gap otherwise they wouldn't be producing them i guess... i mean after all most airliners were built to fill a "size gap".
so lets say your corporate department or even your charter company wants a jet but your business is only catering to 2 or sometimes 3 personnel or customers at a time.
Do you buy a king air C90 or 200 or 350? Do you say "well we really want a jet." and go with a Learjet45 or a citation? because if you do your going to have 7 to 12 seats that are not doing anything on every flight. thats impractical and very costly from a business perspective. ideally you want at least 80% of your seats occupied in order for the flight's costs to be justifiable.
So lets say you buy a piaggio avanti - with its 9 seat cabin, 7 seats will usually be empty, but with the eclipse jet with only 4 or 5 seats there is no empty dead loss factor...
these VLJs are supposed to be smaller, more fuel efficient and faster than dated turboprop equipment.
im not sure exactly which "citationjets" your talking about unless it is the new "citation mustang". I have flown the cessna citation 5 series and it has a max TO weight of about 15,000 to 17,000 lbs.
as far as citations go you have these to choose from (you can convert to Kg if you like)
CitationJet 1 = 10,700 lbs MTOW (barely 700 lbs too heavy for VLJ class)
CitationJet 2 = 12,500 lbs MTOW (2,500 lbs too heavy for VLJ class)
CitationJet 3 = 13,870 lbs MTOW (3,870 lbs too heavy for VLJ class)
Citation 5 = 15,500 lbs MTOW ( 5,500 lbs too heavy for VLJ class)
Citation Encore = 16,300 lbs MTOW (6,300 lb too heavy for VLJ class)
Citation XLS = 30,500 lbs MTOW (20,500 lbs too heavy for VLJ class)
Citation Sovereign= 30,300 lbs MTOW ( 20,300 lbs too heavy for VLJ class)
Citation X = 36,000 lbs MTOW (26,000 lbs too heavy for VLJ class)
the only Cessna product built specifically to qualify as a VLJ that i'm aware of is the New Citation Mustang
barely making it under 10,000 lbs max takeoff weight.
currently every major manufacturer is working on some kind of VLJ aircraft. look at this web page, maybe it can help explain...
http://en.wikipedia.org/wiki/VLJ