Until they have better ticket machines that you can get all tickets on yes.
That of course is entirely achievable - look at SBB or Nederlandse Spoorwegen's machines. And in Italy they manage to cope with compulsory reservations and quota-priced services, and in Germany with train category and route specific pricing. It really isn't hard at all.
Also ticket machines are slow and under-provided, particularly if a customer is not used to them. With my local station only having one machine and one train a hour many times i have had to travel without a ticket because the line is so long. A ticket office is quicker and easier to use.
Both of those can be improved. You can fit two narrow-form TVMs in the space of one ticket window. You can fit faster printers, particularly if we can move away from the credit-card-sized orange card onto different form factors, and/or fit multiple printers (perhaps three) into each machine.
FWIW, what I'd envisage for the future is (in addition to online ticketing):-
Small stations: two TVMs, one on each platform
Medium stations: a number of TVMs, perhaps five, in a central ticketing area by the entrance. One assistance window. Possibly a small fee (£1) for use of the window for things the TVM can do (a list would need to be defined) to keep it free.
Large stations: a bank of many, perhaps 20+, TVMs in a ticketing area plus a few dotted around the station. A travel centre with perhaps 5-6 sit-down desks and a take-a-number queueing system for those requiring detailed advice, again a fee would be chargeable for use of this if you made a request easily obtained from a TVM.
TVMs to have remote video assistance from a call centre. The remote assistance could make the TVM print a "you can't get that here" voucher to remove the fee for listed products.
I would suggest a ticket office fee would be charged for:-
1. Anytime (Day) and (Super) Off Peak (Day) tickets originating from that station for travel on the same day.
2. Local area tickets like Travelcards, GMPTE Rangers etc.
3. Weekly and monthly season tickets up to a specified value.
A fee would not be charged for the purchase of tickets for say 8 or more people travelling together, nor for adding to Railcard groups as the existing groups need to be verified so TVMs won't allow the purchase.
A fee would not be charged for holders of DSB Railcards, nor for anyone stating that a disability prevents use of the TVM. (This might result in a few people lying, however the queues will still be kept down as most people would not sink as low as to lie about a disability).
Annual season tickets are a right nuisance, and I would abolish them to be replaced by a monthly direct debit season ticket available online, by telephone or by post. Season ticket refunds could move to being by post only, as without annuals the need for them would reduce massively.
In the event of there not being a certain specified percentage of TVMs in service, the fee would also be waived.
Euston's setup is not unlike my "large station" proposal, except for the fee, and by making the TVMs the obvious first thing to go to, with the office around the back, works well.