Characters may only buy one lifestyle. This lifestyle truly reflects
the runner’s standard living circumstances. Additional living amenities
such as hotel stays, workshops, safehouses, and so on are handled as
separate costs. Likewise, while lifestyle accounts for the costs of maintaining
a vehicle (or paying for other methods of transportation), it
does not account for the cost of a vehicle itself—that must be purchased
separately.
They could have made it that way with the thought that space is limited in the various metroplexes, so maybe SINners are only allowed to "own" a single dwelling? In character reality however runners never really "own" their lifestyles, rather they pay monthly rent to live there. Who knows why they would put that? While that paragraph in SR4A by itself is quite literal, things change once you look at "Advanced Lifestyle" rules in the Runner's Companion book. Essentially it overrides the SR4A passage.
At some point in their career, every shadowrunner needs a
place to lay low. Having a safe house available (or two or three) can
be invaluable when you’re cooling off after that hot Aztech data
steal. Or, perhaps your runner maintains two lives, partying socialite
by day, covert-ops specialist by night. You might have a family
to support that knows nothing of your illicit activities. Whatever
your reasons, figuring out the costs is fairly simple. Calculate the
point value of each lifestyle separately, determine each lifestyle’s
nuyen cost per the Lifestyle Point/Cost Table, p. 153, and then
add together the separate nuyen costs. (Add the nuyen costs, not
the points, to determine the total cost of the lifestyle)
So there you have it, you can have multiple lifestyles again. I think their thinking was that you have a primary residence that represents "home" for the character, which would explain the "only one" limit in SR4A, with the partial sentence about paying for safehouses separately, which is kinda annoying since they don't give rules for it (or assume the GM would come up with something).
The neat thing about using the advanced lifestyle system is that it allows you to flesh out your doss. It breaks down lifestyles into 5 categories (Comforts, Entertainment, Necessities, Neighborhood, & Security) which let you customize the lifestyle. Basically, you can now figure out how much it costs to have a flat in an abandoned building in the barrens that has a crazy security system (i.e. safehouse #1), or a nice place in a quiet Auburn neighborhood with no furniture (i.e. safehouse #2). They go into further detail about having a SIN vs. being SINless, etc. For example, SINless people can only have up to 7 points on the lifestyle cost table, which is 1100¥, which is somewhere between squatter and low lifestyles.
On a side note, Eric's lifestyle is essentially his RV. Seeing as how he's a SINner of the UCAS, he'd probably be running around the UCAS zone. As part of his background however he's been to other "countries" (CAS, CalFree, etc.) so those nations might have records of his work visas to enter their borders. As such it might be easier for him to go between the zones, but I really don't have any idea about the goings on in Denver (as I never read the sourcebook on that topic) so that's just speculation on my part

-Ingo